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<!doctype linuxdoc system>
<book>

<title> S-Lang Run-Time Library Reference: Version 1.4.0
<author> John E. Davis, <tt>davis@space.mit.edu</tt>
<date> Jan 26, 2003

<toc>

<chapt>Array Functions<p>
<sect><bf>_isnull</bf><label id="_isnull"><p><descrip>
<tag> Synopsis </tag> Check array for NULL elements
<tag> Usage </tag> <tt>Char_Type[] = _isnull (a[])</tt>
<tag> Description </tag>
  This function may be used to test for the presence of NULL elements
  of an array.   Specifically, it returns a <tt>Char_Type</tt> array of
  with the same number of elements and dimensionality of the input
  array.  If an element of the input array is <tt>NULL</tt>, then the
  corresponding element of the output array will be set to <tt>1</tt>,
  otherwise it will be set to <tt>0</tt>.
<tag> Example </tag>
  Set all <tt>NULL</tt> elements of a string array <tt>A</tt> to the empty
  string <tt>""</tt>:
<tscreen><verb>
     A[where(_isnull(A))] = "";
</verb></tscreen>
<tag> Notes </tag>
  It is important to understand the difference between <tt>A==NULL</tt>
  and <tt>_isnull(A)</tt>.  The latter tests all elements of <tt>A</tt>
  against <tt>NULL</tt>, whereas the former only tests <tt>A</tt> itself.
<tag> See Also </tag> <tt>where, array_map</tt>
</descrip><p>

<sect><bf>_reshape</bf><label id="_reshape"><p><descrip>
<tag> Synopsis </tag> Copy an array to a new shape
<tag> Usage </tag> <tt>Array_Type _reshape (Array_Type A, Array_Type I)</tt>
<tag> Description </tag>
  The <tt>_reshape</tt> function creates a copy of an array <tt>A</tt>,
  reshapes it to the form specified by <tt>I</tt> and returns the result.
  The elements of <tt>I</tt> specify the new dimensions of the copy of
  <tt>A</tt> and must be consistent with the number of elements <tt>A</tt>.
<tag> Example </tag>
  If <tt>A</tt> is a <tt>100</tt> element 1-d array, a new array 2-d array of 
  size <tt>20</tt> by <tt>5</tt> may be created from the elements of <tt>A</tt>
  by
<tscreen><verb>
      A = _reshape (A, [20, 5]);
</verb></tscreen>
  In this example, the original array was no longer needed.  Hence, it
  is preferable to make use of the <tt>__tmp</tt> operator to avoid the
  creation of a new array, i.e.,
<tscreen><verb>
      A = _reshape (__tmp(A), [20,5]);
</verb></tscreen>
<tag> Notes </tag>
  The <tt>reshape</tt> function performs a similar function to
  <tt>_reshape</tt>.  In fact, the <tt>_reshape</tt> function could have been
  implemented via:
<tscreen><verb>
     define _reshape (a, i)
     {
        a = @a;     % Make a new copy
        reshape (a, i);
        return a;
     }
</verb></tscreen>
<tag> See Also </tag> <tt>reshape, array_info</tt>
</descrip><p>

<sect><bf>array_info</bf><label id="array_info"><p><descrip>
<tag> Synopsis </tag> Returns information about an array
<tag> Usage </tag> <tt>(Array_Type, Integer_Type, DataType_Type) array_info (Array_Type a)</tt>
<tag> Description </tag>
  The <tt>array_info</tt> function returns information about the array <tt>a</tt>.
  It returns three values: an 1-d integer array array specifying the
  size of each dimension of <tt>a</tt>, the number of dimensions of
  <tt>a</tt>, and the data type of <tt>a</tt>.
<tag> Example </tag>
  The <tt>array_info</tt> function may be used to find the number of rows
  of an array:
<tscreen><verb>
    define num_rows (a)
    {
       variable dims, num_dims, data_type;

       (dims, num_dims, data_type) = array_info (a);
       return dims [0];
    }
</verb></tscreen>
  For 1-d arrays, this information is more easily obtained from the
  <tt>length</tt> function.
<tag> See Also </tag> <tt>typeof, reshape, length, _reshape</tt>
</descrip><p>

<sect><bf>array_map</bf><label id="array_map"><p><descrip>
<tag> Synopsis </tag> Apply a function to each element of an array
<tag> Usage </tag> <tt>Array_Type array_map (type, func, arg0, ...)</tt>
<tscreen><verb>
    DataType_Type type;
    Ref_Type func;
</verb></tscreen>
<tag> Description </tag>
  The <tt>array_map</tt> function may be used to apply a function to each
  element of an array and returns the result as an array of a
  specified type.  The <tt>type</tt> parameter indicates what kind of
  array should be returned and generally corresponds to the return
  type of the function.  The <tt>arg0</tt> parameter should be an array
  and is used to determine the dimensions of the resulting array.  If
  any subsequent arguments correspond to an array of the same size,
  then those array elements will be passed in parallel with the first
  arrays arguments.
<tag> Example </tag>
  The first example illustrates how to apply the <tt>strlen</tt> function
  to an array of strings:
<tscreen><verb>
     S = ["", "Train", "Subway", "Car"];
     L = array_map (Integer_Type, &amp;strlen, S);
</verb></tscreen>
  This is equivalent to:
<tscreen><verb>
     S = ["", "Train", "Subway", "Car"];
     L = Integer_Type [length (S)];
     for (i = 0; i &lt; length (S); i++) L[i] = strlen (S[i]);
</verb></tscreen>
  
  Now consider an example involving the <tt>strcat</tt> function:
<tscreen><verb>
     files = ["slang", "slstring", "slarray"];

     exts = ".c";
     cfiles = array_map (String_Type, &amp;strcat, files, exts);
     % ==&gt; cfiles = ["slang.c slstring.c slarray.c"];

     exts =  [".a",".b",".c"];
     xfiles = array_map (String_Type, &amp;strcat, files, exts);
     % ==&gt; xfiles = ["slang.a", "slstring.b", "slarray.c"];
</verb></tscreen>
<tag> Notes </tag>
  Many mathemetical functions already work transparantly on arrays.
  For example, the following two statements produce identical results:
<tscreen><verb>
     B = sin (A);
     B = array_map (Double_Type, &amp;sin, A);
</verb></tscreen>
<tag> See Also </tag> <tt>array_info, strlen, strcat, sin</tt>
</descrip><p>

<sect><bf>array_sort</bf><label id="array_sort"><p><descrip>
<tag> Synopsis </tag> Sort an array
<tag> Usage </tag> <tt>Array_Type array_sort (Array_Type a [, String_Type or Ref_Type f])</tt>
<tag> Description </tag>
  <tt>array_sort</tt> sorts the array <tt>a</tt> into ascending order and
  returns an integer array that represents the result of the sort. If
  the optional second parameter <tt>f</tt> is present, the function
  specified by <tt>f</tt> will be used to compare elements of <tt>a</tt>;
  otherwise, a built-in sorting function will be used.  

  If <tt>f</tt> is present, then it must be either a string representing
  the name of the comparison function, or a reference to the function.
  The sort function represented by <tt>f</tt> must be a <bf>S-lang</bf>
  user-defined function that takes two arguments.  The function must
  return an integer that is less than zero if the first parameter is
  considered to be less than the second, zero if they are equal, and a
  value greater than zero if the first is greater than the second.

  If the comparision function is not specified, then a built-in comparison
  function appropriate for the data type will be used.  For example,
  if <tt>a</tt> is an array of character strings, then the sort will be
  preformed using <tt>strcmp</tt>.

  The integer array returned by this function is simply an index that
  indicates the order of the sorted array.  The input array <tt>a</tt> is
  not changed.
<tag> Example </tag>
  An array of strings may be sorted using the <tt>strcmp</tt> function
  since it fits the specification for the sorting function described
  above:
<tscreen><verb>
     variable A = String_Type [3];
     A[0] = "gamma"; A[1] = "alpha"; A[2] = "beta";

     variable I = array_sort (A, &amp;strcmp);
</verb></tscreen>
  Alternatively, one may use
<tscreen><verb>
     variable I = array_sort (A);     
</verb></tscreen>
  to use the built-in comparison function.

  After the <tt>array_sort</tt> has executed, the variable <tt>I</tt> will
  have the values <tt>[2, 0, 1]</tt>.  This array can be used to
  re-shuffle the elements of <tt>A</tt> into the sorted order via the
  array index expression <tt>A = A[I]</tt>.
<tag> See Also </tag> <tt>strcmp</tt>
</descrip><p>

<sect><bf>init_char_array</bf><label id="init_char_array"><p><descrip>
<tag> Synopsis </tag> Initialize an array of characters
<tag> Usage </tag> <tt>init_char_array (Array_Type a, String_Type s)</tt>
<tag> Description </tag>
  The <tt>init_char_array</tt> function may be used to initialize a
  character array <tt>a</tt> by setting the elements of the array
  <tt>a</tt> to the corresponding characters of the string <tt>s</tt>.
<tag> Example </tag>
  The statements
<tscreen><verb>
     variable a = Char_Type [10];
     init_char_array (a, "HelloWorld");
</verb></tscreen>
   creates an character array and initializes its elements to the
   characters in the string <tt>"HelloWorld"</tt>.
<tag> Notes </tag>
   The character array must be large enough to hold all the characters
   of the initialization string.
<tag> See Also </tag> <tt>bstring_to_array, strlen, strcat</tt>
</descrip><p>

<sect><bf>length</bf><label id="length"><p><descrip>
<tag> Synopsis </tag> Get the length of an object
<tag> Usage </tag> <tt>Integer_Type length (obj)</tt>
<tag> Description </tag>
  The <tt>length</tt> function may be used to get information about the
  length of an object.  For simple scalar data-types, it returns <tt>1</tt>.
  For arrays, it returns the total number of elements of the array.
<tag> Notes </tag>
  If <tt>obj</tt> is a string, <tt>length</tt> returns <tt>1</tt> because a
  <tt>String_Type</tt> object is considered to be a scalar.  To get the
  number of characters in a string, use the <tt>strlen</tt> function.
<tag> See Also </tag> <tt>array_info, typeof, strlen</tt>
</descrip><p>

<sect><bf>max</bf><label id="max"><p><descrip>
<tag> Synopsis </tag> Get the maximum value of an array
<tag> Usage </tag> <tt>result = max (Array_Type a [,Int_Type dim])</tt>
<tag> Description </tag>
  The <tt>max</tt> function examines the elements of a numeric array and
  returns the value of the largest element.  If a second argument is
  given, then it specifies the dimension of the array to be searched.
  In this case, an array of dimension one less than that of the input array
  will be returned with the corresponding elements in the specified
  dimension replaced by the minimum value in that dimension.
<tag> Example </tag>
  Consider the 2-d array
<tscreen><verb>
      1       2       3       4       5
      6       7       8       9       10
</verb></tscreen>
  generated by
<tscreen><verb>
      a = _reshape ([1:10], [2, 5]);
</verb></tscreen>
  Then <tt>max(a)</tt> will return <tt>10</tt>, and <tt>max(a,0)</tt> will return
  a 1-d array with elements
<tscreen><verb>
      6       7       8       9       10
</verb></tscreen>
<tag> See Also </tag> <tt>max, sum, reshape</tt>
</descrip><p>

<sect><bf>min</bf><label id="min"><p><descrip>
<tag> Synopsis </tag> Get the minimum value of an array
<tag> Usage </tag> <tt>result = min (Array_Type a [,Int_Type dim])</tt>
<tag> Description </tag>
  The <tt>min</tt> function examines the elements of a numeric array and
  returns the value of the smallest element.  If a second argument is
  given, then it specifies the dimension of the array to be searched.
  In this case, an array of dimension one less than that of the input array
  will be returned with the corresponding elements in the specified
  dimension replaced by the minimum value in that dimension.
<tag> Example </tag>
  Consider the 2-d array
<tscreen><verb>
      1       2       3       4       5
      6       7       8       9       10
</verb></tscreen>
  generated by
<tscreen><verb>
      a = _reshape ([1:10], [2, 5]);
</verb></tscreen>
  Then <tt>min(a)</tt> will return <tt>1</tt>, and <tt>min(a,0)</tt> will return
  a 1-d array with elements
<tscreen><verb>
      1        2       3       4       5
</verb></tscreen>
<tag> See Also </tag> <tt>max, sum, reshape</tt>
</descrip><p>

<sect><bf>reshape</bf><label id="reshape"><p><descrip>
<tag> Synopsis </tag> Reshape an array
<tag> Usage </tag> <tt>reshape (Array_Type A, Array_Type I)</tt>
<tag> Description </tag>
  The <tt>reshape</tt> function changes the size of <tt>A</tt> to have the size
  specified by the 1-d integer array <tt>I</tt>.  The elements of <tt>I</tt>
  specify the new dimensions of <tt>A</tt> and must be consistent with
  the number of elements <tt>A</tt>.
<tag> Example </tag>
  If <tt>A</tt> is a <tt>100</tt> element 1-d array, it can be changed to a
  2-d <tt>20</tt> by <tt>5</tt> array via
<tscreen><verb>
      reshape (A, [20, 5]);
</verb></tscreen>
  However, <tt>reshape(A, [11,5])</tt> will result in an error because
  the the <tt>[11,5]</tt> array specifies <tt>55</tt> elements.
<tag> Notes </tag>
  Since <tt>reshape</tt> modifies the shape of an array, and arrays are
  treated as references, then all references to the array will
  reference the new shape.  If this effect is unwanted, then use the 
  <tt>_reshape</tt> function instead.
<tag> See Also </tag> <tt>_reshape, array_info</tt>
</descrip><p>

<sect><bf>sum</bf><label id="sum"><p><descrip>
<tag> Synopsis </tag> Sum over the elements of an array
<tag> Usage </tag> <tt>result = sum (Array_Type a [, Int_Type dim])</tt>
<tag> Description </tag>
  The <tt>sum</tt> function sums over the elements of a numeric array and
  returns its result.  If a second argument is given, then it
  specifies the dimension of the array to be summed over.  In this
  case, an array of dimension one less than that of the input array
  will be returned.

  If the input array is an integer type, then the resulting value will
  be a <tt>Double_Type</tt>.  If the input array is a <tt>Float_Type</tt>,
  then the result will be a <tt>Float_Type</tt>.
<tag> Example </tag>
  The mean of an array <tt>a</tt> of numbers is
<tscreen><verb>
    sum(a)/length(a)
</verb></tscreen>
<tag> See Also </tag> <tt>transpose, reshape</tt>
</descrip><p>

<sect><bf>transpose</bf><label id="transpose"><p><descrip>
<tag> Synopsis </tag> Transpose an array
<tag> Usage </tag> <tt>Array_Type transpose (Array_Type a)</tt>
<tag> Description </tag>
  The <tt>transpose</tt> function returns the transpose of a specified
  array.  By definition, the transpose of an array, say one with
  elements <tt>a[i,j,...k]</tt> is an array whose elements are
  <tt>a[k,...,j,i]</tt>.
<tag> See Also </tag> <tt>_reshape, reshape, sum, array_info</tt>
</descrip><p>

<sect><bf>where</bf><label id="where"><p><descrip>
<tag> Synopsis </tag> Get indices where an integer array is non-zero
<tag> Usage </tag> <tt>Array_Type where (Array_Type a)</tt>
<tag> Description </tag>
  The <tt>where</tt> function examines an numeric array <tt>a</tt> and
  returns an integer array giving the indices of <tt>a</tt>
  where the corresponding element of <tt>a</tt> is non-zero.
  
  Although this function may appear to be simple or even trivial, it
  is arguably one of the most important and powerful functions for
  manipulating arrays.
<tag> Example </tag>
  Consider the following:
<tscreen><verb>
    variable X = [0.0:10.0:0.01];
    variable A = sin (X);
    variable I = where (A &lt; 0.0);
    A[I] = cos (X) [I];
</verb></tscreen>
  Here the variable <tt>X</tt> has been assigned an array of doubles
  whose elements range from <tt>0.0</tt> through <tt>10.0</tt> in
  increments of <tt>0.01</tt>.  The second statement assigns <tt>A</tt> to
  an array whose elements are the <tt>sin</tt> of the elements of <tt>X</tt>.
  The third statement uses the where function to get the indices of
  the elements of <tt>A</tt> that are less than <tt>0.0</tt>.  Finally, the
  last statement substitutes into <tt>A</tt> the <tt>cos</tt> of the
  elements of <tt>X</tt> at the positions of <tt>A</tt> where the
  corresponding <tt>sin</tt> is less than <tt>0</tt>.  The end result is
  that the elements of <tt>A</tt> are a mixture of sines and cosines.
<tag> See Also </tag> <tt>array_info, sin, cos</tt>
</descrip><p>


<chapt>Associative Array Functions<p>
<sect><bf>assoc_delete_key</bf><label id="assoc_delete_key"><p><descrip>
<tag> Synopsis </tag> Delete a key from an Associative Array
<tag> Usage </tag> <tt>assoc_delete_key (Assoc_Type a, String_Type k)</tt>
<tag> Description </tag>
  The <tt>assoc_delete_key</tt> function deletes a key given by <tt>k</tt>
  from the associative array <tt>a</tt>.  If the specified key does not
  exist in <tt>a</tt>, then this function has no effect.
<tag> See Also </tag> <tt>assoc_key_exists, assoc_get_keys</tt>
</descrip><p>

<sect><bf>assoc_get_keys</bf><label id="assoc_get_keys"><p><descrip>
<tag> Synopsis </tag> Return all the key names of an Associative Array
<tag> Usage </tag> <tt>String_Type[] assoc_get_keys (Assoc_Type a)</tt>
<tag> Description </tag>
  This function returns all the key names of an associative array
  <tt>a</tt> as an ordinary one dimensional array of strings.  If the
  associative array contains no keys, an empty array will be returned.
<tag> Example </tag>
  The following function computes the number of keys in an associative
  array:
<tscreen><verb>
      define get_num_elements (a)
      {
         return length (assoc_get_keys (a));
      }
</verb></tscreen>
<tag> See Also </tag> <tt>assoc_get_values, assoc_key_exists, assoc_delete_key, length</tt>
</descrip><p>

<sect><bf>assoc_get_values</bf><label id="assoc_get_values"><p><descrip>
<tag> Synopsis </tag> Return all the values of an Associative Array
<tag> Usage </tag> <tt>Array_Type assoc_get_keys (Assoc_Type a)</tt>
<tag> Description </tag>
  This function returns all the values in the associative array
  <tt>a</tt> as an array of proper type.  If the associative array
  contains no keys, an empty array will be returned.
<tag> Example </tag>
  Suppose that <tt>a</tt> is an associative array of type
  <tt>Integer_Type</tt>, i.e., it was created via
<tscreen><verb>
      variable a = Assoc_Type[Integer_Type];
</verb></tscreen>
  The the following may be used to print the values of the array in
  ascending order:
<tscreen><verb>
      static define int_sort_fun (x, y)
      {
         return sign (x - y);
      }
      define sort_and_print_values (a)
      {
         variable i, v;
	 
	 v = assoc_get_values (a);
	 i = array_sort (v, &amp;int_sort_fun);
	 v = v[i];
	 foreach (v)
	   {
	      variable vi = ();
	      () = fprintf (stdout, "%d\n", vi);
	   }
      }
</verb></tscreen>
<tag> See Also </tag> <tt>assoc_get_values, assoc_key_exists, assoc_delete_key, array_sort</tt>
</descrip><p>

<sect><bf>assoc_key_exists</bf><label id="assoc_key_exists"><p><descrip>
<tag> Synopsis </tag> Check to see whether a key exists in an Associative Array
<tag> Usage </tag> <tt>Integer_Type assoc_key_exists (Assoc_Type a, String_Type k)</tt>
<tag> Description </tag>
  The <tt>assoc_key_exists</tt> function may be used to determine whether
  or not a specified key <tt>k</tt> exists in an associative array <tt>a</tt>.
  It returns <tt>1</tt> if the key exists, or <tt>0</tt> if it does not.
<tag> See Also </tag> <tt>assoc_get_keys, assoc_get_values, assoc_delete_key</tt>
</descrip><p>


<chapt>Functions that Operate on Strings<p>
<sect><bf>Sprintf</bf><label id="Sprintf"><p><descrip>
<tag> Synopsis </tag> Format objects into a string
<tag> Usage </tag> <tt>String_Type Sprintf (String_Type format, ..., Integer_Type n)</tt>
<tag> Description </tag>
  <tt>Sprintf</tt> formats a string from <tt>n</tt> objects according to
  <tt>format</tt>.  Unlike <tt>sprintf</tt>, the <tt>Sprintf</tt> function
  requires the number of items to format.
  
  The format string is a C library <tt>sprintf</tt> style format
  descriptor.  Briefly, the format string may consist of ordinary
  characters (not including the <tt>%</tt> character), which are copied
  into the output string as-is, and a conversion specification
  introduced by the <tt>%</tt> character.  The <tt>%</tt> character must be
  followed by at least one other character to specify the conversion:
<tscreen><verb>
     s    value is a string
     f    value is a floating point number
     e    print float in exponential form, e.g., 2.345e08
     g    print float as e or g, depending upon its value
     c    value is an ascii character
     %    print the percent character
     d    print a signed decimal integer
     u    print an unsigned decimal integer
     o    print an integer as octal
     X    print an integer as hexadecimal
     S    convert value to a string and format as string
</verb></tscreen>
  Note that <tt>%S</tt> is a <bf>S-lang</bf> extension which will cause the value
  to be formatted as string.  In fact, <tt>sprintf("%S",x)</tt> is
  equivalent to <tt>sprintf("%s",string(x))</tt>.
<tscreen><verb>
     s = Sprintf("%f is greater than %f but %s is better than %s\n",
                 PI, E, "Cake" "Pie", 4);
</verb></tscreen>
  The final argument to <tt>Sprintf</tt> is the number of items to format; in
  this case, there are 4 items.
<tag> See Also </tag> <tt>sprintf, string, sscanf</tt>
</descrip><p>

<sect><bf>create_delimited_string</bf><label id="create_delimited_string"><p><descrip>
<tag> Synopsis </tag> Concatenate strings using a delimiter
<tag> Usage </tag> <tt>String_Type create_delimited_string (delim, s_1, s_2, ..., s_n, n)</tt>
<tscreen><verb>
    String_Type delim, s_1, ..., s_n
    Integer_Type n
</verb></tscreen>
<tag> Description </tag>
  <tt>create_delimited_string</tt> performs a concatenation operation on
  the <tt>n</tt> strings <tt>s_1</tt>, ...,<tt>s_n</tt>, using the string
  <tt>delim</tt> as a delimiter.  The resulting string is equivalent to
  one obtained via
<tscreen><verb>
      s_1 + delim + s_2 + delim + ... + s_n
</verb></tscreen>
<tag> Example </tag>
  One use for this function is to construct path names, e.g.,
<tscreen><verb>
    create_delimited_string ("/", "user", "local", "bin", 3);
</verb></tscreen>
  will produce <tt>"usr/local/bin"</tt>.
<tag> Notes </tag>
  The expression <tt>strcat(a,b)</tt> is equivalent to
  <tt>create_delimited_string("", a, b, 2)</tt>.
<tag> See Also </tag> <tt>strjoin, is_list_element, extract_element, strchop, strcat</tt>
</descrip><p>

<sect><bf>extract_element</bf><label id="extract_element"><p><descrip>
<tag> Synopsis </tag> Extract the nth element of a string with delimiters
<tag> Usage </tag> <tt>String_Type extract_element (String_Type list, Integer_Type nth, Integer_Type delim);</tt>
<tag> Description </tag>
  The <tt>extract_element</tt> function may be used to extract the
  <tt>nth</tt> element of the <tt>delim</tt> delimited list of strings
  <tt>list</tt>.  The function will return the <tt>nth</tt> element of the
  list, unless <tt>nth</tt> specifies more elements than the list
  contains, in which case <tt>NULL</tt> will be returned.
  Elements in the list are numbered from <tt>0</tt>.
<tag> Example </tag>
  The expression
<tscreen><verb>
     extract_element ("element 0, element 1, element 2", 1, ',')
</verb></tscreen>
  returns the string <tt>" element 1"</tt>, whereas
<tscreen><verb>
     extract_element ("element 0, element 1, element 2", 1, ' ')
</verb></tscreen>
  returns <tt>"0,"</tt>.

  The following function may be used to compute the number of elements
  in the list:
<tscreen><verb>
     define num_elements (list, delim)
     {
        variable nth = 0;
        while (NULL != extract_element (list, nth, delim))
          nth++;
        return nth;
     }
</verb></tscreen>

  Alternatively, the <tt>strchop</tt> function may be more useful.  In
  fact, <tt>extract_element</tt> may be expressed in terms of the
  function <tt>strchop</tt> as
<tscreen><verb>
    define extract_element (list, nth, delim)
    {
       list = strchop(list, delim, 0);
       if (nth &gt;= length (list))
         return NULL;
       else
         return list[nth];
    }
</verb></tscreen>
   and the <tt>num_elements</tt> function used above may be recoded more
   simply as:
<tscreen><verb>
    define num_elements (list, delim)
    {
       return length (strchop (length, delim, 0));
    }
</verb></tscreen>
<tag> See Also </tag> <tt>is_list_element, is_substr, strtok, strchop, create_delimited_string</tt>
</descrip><p>

<sect><bf>is_list_element</bf><label id="is_list_element"><p><descrip>
<tag> Synopsis </tag> Test whether a delimited string contains a specific element
<tag> Usage </tag> <tt>Integer_Type is_list_element (String_Type list, String_Type elem, Integer_Type delim)</tt>
<tag> Description </tag>
  The <tt>is_list_element</tt> function may be used to determine whether
  or not a delimited list of strings, <tt>list</tt>, contains the element
  <tt>elem</tt>.  If <tt>elem</tt> is not an element of <tt>list</tt>, the function
  will return zero, otherwise, it returns 1 plus the matching element
  number.
<tag> Example </tag>
  The expression
<tscreen><verb>
     is_list_element ("element 0, element 1, element 2", "0,", ' ');
</verb></tscreen>
  returns <tt>2</tt> since <tt>"0,"</tt> is element number one of the list
  (numbered from zero).
<tag> See Also </tag> <tt>extract_element, is_substr, create_delimited_string</tt>
</descrip><p>

<sect><bf>is_substr</bf><label id="is_substr"><p><descrip>
<tag> Synopsis </tag> Test for a specified substring within a string.
<tag> Usage </tag> <tt>Integer_Type is_substr (String_Type a, String_Type b)</tt>
<tag> Description </tag>
  This function may be used to determine if <tt>a</tt> contains the
  string <tt>b</tt>.  If it does not, the function returns 0; otherwise it
  returns the position of the first occurance of <tt>b</tt> in <tt>a</tt>.
<tag> Notes </tag>
  It is important to remember that the first character of a string
  corresponds to a position value of <tt>1</tt>.
<tag> See Also </tag> <tt>substr, string_match, strreplace</tt>
</descrip><p>

<sect><bf>make_printable_string</bf><label id="make_printable_string"><p><descrip>
<tag> Synopsis </tag> Format a string suitable for parsing
<tag> Usage </tag> <tt>String_Type make_printable_string(String_Type str)</tt>
<tag> Description </tag>
  This function formats a string in such a way that it may be used as
  an argument to the <tt>eval</tt> function.  The resulting string is
  identical to <tt>str</tt> except that it is enclosed in double quotes and the
  backslash, newline, and double quote characters are expanded.
<tag> See Also </tag> <tt>eval, str_quote_string</tt>
</descrip><p>

<sect><bf>sprintf</bf><label id="sprintf"><p><descrip>
<tag> Synopsis </tag> Format objects into a string
<tag> Usage </tag> <tt>String sprintf (String format, ...);</tt>
<tag> Description </tag>
  This function performs a similar task as the C function with the same
  name.  It differs from the <bf>S-lang</bf> function <tt>Sprintf</tt> in that it
  does not require the number of items to format.
  See the documentation for <tt>Sprintf</tt> for more information.
<tag> See Also </tag> <tt>Sprintf, string, sscanf, vmessage</tt>
</descrip><p>

<sect><bf>sscanf</bf><label id="sscanf"><p><descrip>
<tag> Synopsis </tag> Parse a formatted string
<tag> Usage </tag> <tt>Int_Type sscanf (s, fmt, r1, ... rN)</tt>
<tscreen><verb>
    String_Type s, fmt;
    Ref_Type r1, ..., rN
</verb></tscreen>
<tag> Description </tag>
 The <tt>sscanf</tt> function parses the string <tt>s</tt> according to the
 format <tt>fmt</tt> and sets the variables whose references are given by
 <tt>r1</tt>, ..., <tt>rN</tt>.  The function returns the number of
 references assigned, or <tt>-1</tt> upon error.
 
 The format string <tt>fmt</tt> consists of ordinary characters and
 conversion specifiers.  A conversion specifier begins with the
 special character <tt>%</tt> and is described more fully below.  A white
 space character in the format string matches any amount of whitespace
 in the input string.  Parsing of the format string stops whenever a
 match fails.

 The <tt>%</tt> is used to denote a conversion specifier whose general
 form is given by <tt>%[*][width][type]format</tt> where the brackets
 indicate optional items.  If <tt>*</tt> is present, then the conversion
 will be performed by no assignment to a reference will be made.  The
 <tt>width</tt> specifier specifies the maximum field width to use for
 the conversion.  The <tt>type</tt> modifier is used to indicate size of
 the object, e.g., a short integer, as follows. 
 
 If <em>type</em> is given as the character <tt>h</tt>, then if the format
 conversion is for an integer (<tt>dioux</tt>), the object assigned will
 be a short integer.  If <em>type</em> is <tt>l</tt>, then the conversion
 will be to a long integer for integer conversions, or to a double
 precession floating point number for floating point conversions.

 The format specifier is a character that specifies the conversion:
<tscreen><verb>
       %     Matches a literal percent character.  No assigment is
             performed.
       d     Matches a signed decimal integer.
       D     Matches a long decimal integer (equiv to `ld')
       u     Matches an unsigned decimal integer
       U     Matches an unsigned long decimal integer (equiv to `lu')
       i     Matches either a hexidecimal integer, decimal integer, or 
             octal integer.
       I     Equivalent to `li'.
       x     Matches a hexidecimal integer.
       X     Matches a long hexidecimal integer (same as `lx').
       e,f,g Matches a decimal floating point number (Float_Type).
       E,F,G Matches a double precision floating point number, same as `lf'.
       s     Matches a string of non-whitespace characters (String_Type).
       c     Matches one character.  If width is given, width
             characters are matched.
       n     Assigns the number of characters scanned so far.
       [...] Matches zero or more characters from the set of characters
             enclosed by the square brackets.  If '^' is given as the
             first character, then the complement set is matched. 
</verb></tscreen>
<tag> Example </tag>
 Suppose that <tt>s</tt> is <tt>"Coffee: (3,4,12.4)"</tt>.  Then
<tscreen><verb>
    n = sscanf (s, "%[a-zA-Z]: (%d,%d,%lf)", &amp;item, &amp;x, &amp;y, &amp;z);
</verb></tscreen>
 will set <tt>n</tt> to <tt>4</tt>, <tt>item</tt> to <tt>"Coffee"</tt>, <tt>x</tt> to <tt>3</tt>,
 <tt>y</tt> to <tt>4</tt>, and <tt>z</tt> to the double precision number
 <tt>12.4</tt>.  However,
<tscreen><verb>
    n = sscanf (s, "%s: (%d,%d,%lf)", &amp;item, &amp;x, &amp;y, &amp;z);
</verb></tscreen>
 will set <tt>n</tt> to <tt>1</tt>, <tt>item</tt> to <tt>"Coffee:"</tt> and the
 remaining variables will not be assigned.
<tag> See Also </tag> <tt>sprintf, unpack, string, atof, int, integer, string_match</tt>
</descrip><p>

<sect><bf>str_delete_chars</bf><label id="str_delete_chars"><p><descrip>
<tag> Synopsis </tag> Delete characters from a string
<tag> Usage </tag> <tt>String_Type str_delete_chars (String_Type str, String_Type del_set</tt>
<tag> Description </tag>
  This function may be used to delete the set of characters specified
  by <tt>del_set</tt> from the string <tt>str</tt>.  The result is returned.
<tag> Example </tag>
<tscreen><verb>
    str = str_delete_chars (str, "^A-Za-z");
</verb></tscreen>
  will remove all characters except <tt>A-Z</tt> and <tt>a-z</tt> from
  <tt>str</tt>.
</descrip><p>

<sect><bf>str_quote_string</bf><label id="str_quote_string"><p><descrip>
<tag> Synopsis </tag> Escape characters in a string.
<tag> Usage </tag> <tt>String_Type str_quote_string(String_Type str, String_Type qlis, Integer_Type quote)</tt>
<tag> Description </tag>
  The <tt>str_quote_string</tt> returns a string identical to <tt>str</tt>
  except that all characters in the set specified by the string
  <tt>qlis</tt> are escaped with the <tt>quote</tt> character, including the
  quote character itself.   This function is useful for making a
  string that can be used in a regular expression.
<tag> Example </tag>
  Execution of the statements
<tscreen><verb>
   node = "Is it [the coat] really worth $100?";
   tag = str_quote_string (node, "\\^$[]*.+?", '\\');
</verb></tscreen>
  will result in <tt>tag</tt> having the value:
<tscreen><verb>
    Is it \[the coat\] really worth \$100\?
</verb></tscreen>
<tag> See Also </tag> <tt>str_uncomment_string, make_printable_string</tt>
</descrip><p>

<sect><bf>str_replace</bf><label id="str_replace"><p><descrip>
<tag> Synopsis </tag> Replace a substring of a string
<tag> Usage </tag> <tt>Integer_Type str_replace (String_Type a, String_Type b, String_Type c)</tt>
<tag> Description </tag>
  The <tt>str_replace</tt> function replaces the first occurance of <tt>b</tt> in
  <tt>a</tt> with <tt>c</tt> and returns an integer that indicates whether a
  replacement was made or not. If <tt>b</tt> does not occur in <tt>a</tt>, zero is
  returned.  However, if <tt>b</tt> occurs in <tt>a</tt>, a non-zero integer is
  returned as well as the new string resulting from the replacement.
<tag> Notes </tag>
  This function has been superceded by <tt>strreplace</tt>.
<tag> See Also </tag> <tt>strreplace</tt>
</descrip><p>

<sect><bf>str_uncomment_string</bf><label id="str_uncomment_string"><p><descrip>
<tag> Synopsis </tag> Remove comments from a string
<tag> Usage </tag> <tt>String_Type str_uncomment_string(String_Type s, String_Type beg, String_Type end)</tt>
<tag> Description </tag>
  This function may be used to remove comments from a string <tt>s</tt>.
  The parameters, <tt>beg</tt> and <tt>end</tt>, are strings of equal length
  whose corresponding characters specify the begin and end comment
  characters, respectively.  It returns the uncommented string.
<tag> Example </tag>
  The expression
<tscreen><verb>
     str_uncomment_string ("Hello (testing) 'example' World", "'(", "')")
</verb></tscreen>
  returns the string <tt>"Hello   World"</tt>.
<tag> Notes </tag>
  This routine does not handle multicharacter comment delimiters and it
  assumes that comments are not nested.
<tag> See Also </tag> <tt>str_quote_string</tt>
</descrip><p>

<sect><bf>strcat</bf><label id="strcat"><p><descrip>
<tag> Synopsis </tag> Concatenate strings
<tag> Usage </tag> <tt>String_Type strcat (String_Type a_1, ...,  String_Type a_N)</tt>
<tag> Description </tag>
   The <tt>strcat</tt> function concatenates its N <tt>String_Type</tt>
   arguments <tt>a_1</tt>, ... <tt>a_N</tt> together and returns the result.
<tag> Example </tag>
<tscreen><verb>
    strcat ("Hello", " ", "World");
</verb></tscreen>
   produces the string <tt>"Hello World"</tt>.
<tag> Notes </tag>
   This function is equivalent to the binary operation <tt>a_1+...+a_N</tt>.
   However, <tt>strcat</tt> is much faster making it the preferred method
   to concatenate string.
<tag> See Also </tag> <tt>sprintf, create_delimited_string</tt>
</descrip><p>

<sect><bf>strchop</bf><label id="strchop"><p><descrip>
<tag> Synopsis </tag> Chop or split a string into substrings.
<tag> Usage </tag> <tt>String_Type[] strchop (String_Type str, Integer_Type delim, Integer_Type quote)</tt>
<tag> Description </tag>
   The <tt>strchop</tt> function may be used to split-up a string
   <tt>str</tt> that consists of substrings delimited by the character
   specified by <tt>delim</tt>.  If the integer <tt>quote</tt> is non-zero,
   it will be taken as a quote character for the delimiter.  The
   function returns the substrings as an array.
<tag> Example </tag>
   The following function illustrates how to sort a comma separated
   list of strings:
<tscreen><verb>
     define sort_string_list (a)
     { 
        variable i, b, c;
        b = strchop (a, ',', 0);
        
        i = array_sort (b, &amp;strcmp);
        b = b[i];   % rearrange
        
        % Convert array back into comma separated form
        return strjoin (b, ",");
     }
</verb></tscreen>
<tag> Notes </tag>
   The semantics of this <tt>strchop</tt> and <tt>strchopr</tt> have been
   changed since version 1.2.x of the interpreter.  Old versions of
   these functions returned the values on the stack, which meant that
   one could not chop up arbitrarily long strings that consist of
   many substrings.
   
   The function <tt>strchopr</tt> should be used if it is desired to have
   the string chopped-up in the reverse order.
<tag> See Also </tag> <tt>strchopr, extract_element, strjoin, strtok</tt>
</descrip><p>

<sect><bf>strchopr</bf><label id="strchopr"><p><descrip>
<tag> Synopsis </tag> Chop or split a string into substrings.
<tag> Usage </tag> <tt>String_Type[] strchopr (String_Type str, String_Type delim, String_Type quote)</tt>
<tag> Description </tag>
  This routine performs exactly the same function as <tt>strchop</tt> except
  that it returns the substrings in the reverse order.  See the
  documentation for <tt>strchop</tt> for more information.
<tag> See Also </tag> <tt>strchop, extract_element, strtok, strjoin</tt>
</descrip><p>

<sect><bf>strcmp</bf><label id="strcmp"><p><descrip>
<tag> Synopsis </tag> Compare two strings
<tag> Usage </tag> <tt>Interpret strcmp (String_Type a, String_Type b)</tt>
<tag> Description </tag>
   The <tt>strcmp</tt> function may be used to perform a case-sensitive
   string comparison, in the lexicongraphic sense, on strings <tt>a</tt> and
   <tt>b</tt>.  It returns 0 if the strings are identical, a negative integer
   if <tt>a</tt> is less than <tt>b</tt>, or a positive integer if <tt>a</tt> is greater
   than <tt>b</tt>.
<tag> Example </tag>
   The <tt>strup</tt> function may be used to perform a case-insensitive
   string comparison:
<tscreen><verb>
    define case_insensitive_strcmp (a, b)
    {
      return strcmp (strup(a), strup(b));
    }
</verb></tscreen>
<tag> Notes </tag>
   One may also use one of the binary comparison operators, e.g.,
   <tt>a &gt; b</tt>.
<tag> See Also </tag> <tt>strup, strncmp</tt>
</descrip><p>

<sect><bf>strcompress</bf><label id="strcompress"><p><descrip>
<tag> Synopsis </tag> Remove excess whitespace characters from a string
<tag> Usage </tag> <tt>String_Type strcompress (String_Type s, String_Type white)</tt>
<tag> Description </tag>
  The <tt>strcompress</tt> function compresses the string <tt>s</tt> by
  replacing a sequence of one or more characters from the set
  <tt>white</tt> by the first character of <tt>white</tt>. In addition, it
  also removes all leading and trailing characters from <tt>s</tt> that
  are part of <tt>white</tt>.
<tag> Example </tag>
  The expression
<tscreen><verb>
    strcompress (",;apple,,cherry;,banana", ",;");
</verb></tscreen>
  returns the string <tt>"apple,cherry,banana"</tt>.
<tag> See Also </tag> <tt>strtrim, strtrans</tt>
</descrip><p>

<sect><bf>string_match</bf><label id="string_match"><p><descrip>
<tag> Synopsis </tag> Match a string against a regular expression
<tag> Usage </tag> <tt>Integer_Type string_match(String_Type str, String_Type pat, Integer_Type pos)</tt>
<tag> Description </tag>
  The <tt>string_match</tt> function returns zero if <tt>str</tt> does not
  match regular expression specified by <tt>pat</tt>.  This function
  performs the match starting at position <tt>pos</tt> (numbered from 1) in
  <tt>str</tt>.  This function returns the position of the start of the
  match.  To find the exact substring actually matched, use
  <tt>string_match_nth</tt>.
<tag> See Also </tag> <tt>string_match_nth, strcmp, strncmp</tt>
</descrip><p>

<sect><bf>string_match_nth</bf><label id="string_match_nth"><p><descrip>
<tag> Synopsis </tag> Get the result of the last call to string_match
<tag> Usage </tag> <tt>(Integer_Type, Integer_Type) = string_match_nth(Integer_Type nth)</tt>
<tag> Description </tag>
  The <tt>string_match_nth</tt> function returns two integers describing
  the result of the last call to <tt>string_match</tt>.  It returns both
  the offset into the string and the length of characters matches by
  the <tt>nth</tt> submatch.

  By convention, <tt>nth</tt> equal to zero means the entire match.
  Otherwise, <tt>nth</tt> must be an integer with a value 1 through 9,
  and refers to the set of characters matched by the <tt>nth</tt> regular
  expression enclosed by the pairs <tt>\(, \)</tt>.
<tag> Example </tag>
  Consider:
<tscreen><verb>
     variable matched, pos, len;
     matched = string_match("hello world", "\\([a-z]+\\) \\([a-z]+\\)", 1);
     if (matched) (pos, len) = string_match_nth(2);
</verb></tscreen>
  This will set <tt>matched</tt> to 1 since a match will be found at the
  first position, <tt>pos</tt> to 6 since <tt>w</tt> is offset 6 characters
  from the beginning of the string, and <tt>len</tt> to 5 since
  <tt>"world"</tt> is 5 characters long.
<tag> Notes </tag>
  The position offset is <em>not</em> affected by the value of the offset
  parameter to the <tt>string_match</tt> function. For example, if the
  value of the last parameter to the <tt>string_match</tt> function had
  been 3, <tt>pos</tt> would still have been set to 6.

  Note also that <tt>string_match_nth</tt> returns the <em>offset</em> from
  the beginning of the string and not the position of the match.
<tag> See Also </tag> <tt>string_match</tt>
</descrip><p>

<sect><bf>strjoin</bf><label id="strjoin"><p><descrip>
<tag> Synopsis </tag> Concatenate elements of a string array
<tag> Usage </tag> <tt>String_Type strjoin (Array_Type a, String_Type delim)</tt>
<tag> Description </tag>
   The <tt>strjoin</tt> function operates on an array of strings by joining
   successive elements together separated with a delimiter <tt>delim</tt>.
   If <tt>delim</tt> is the empty string <tt>""</tt>, then the result will
   simply be the concatenation of the elements.
<tag> Example </tag>
   Suppose that
<tscreen><verb>
      days = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat","Sun"];
</verb></tscreen>
   Then <tt>strjoin (days,"+")</tt> will produce
   <tt>"Sun+Mon+Tue+Wed+Thu+Fri+Sat+Sun"</tt>.  Similarly,
   <tt>strjoin (["","",""], "X")</tt> will produce <tt>"XX"</tt>.
<tag> See Also </tag> <tt>create_delimited_string, strchop, strcat</tt>
</descrip><p>

<sect><bf>strlen</bf><label id="strlen"><p><descrip>
<tag> Synopsis </tag> Compute the length of a string
<tag> Usage </tag> <tt>Integer_Type strlen (String_Type a)</tt>
<tag> Description </tag>
   The <tt>strlen</tt> function may be used to compute the length of a string.
<tag> Example </tag>
   After execution of
<tscreen><verb>
   variable len = strlen ("hello");
</verb></tscreen>
   <tt>len</tt> will have a value of <tt>5</tt>.
<tag> See Also </tag> <tt>bstrlen, length, substr</tt>
</descrip><p>

<sect><bf>strlow</bf><label id="strlow"><p><descrip>
<tag> Synopsis </tag> Convert a string to lowercase
<tag> Usage </tag> <tt>String_Type strlow (String_Type s)</tt>
<tag> Description </tag>
  The <tt>strlow</tt> function takes a string <tt>s</tt> and returns another
  string identical to <tt>s</tt> except that all upper case characters
  that comprise <tt>s</tt> will be converted to lower case.
<tag> Example </tag>
  The function
<tscreen><verb>
    define Strcmp (a, b)
    {
      return strcmp (strlow (a), strlow (b));
    }
</verb></tscreen>
  performs a case-insensitive comparison operation of two strings by
  converting them to lower case first.
<tag> See Also </tag> <tt>strup, tolower, strcmp, strtrim, define_case</tt>
</descrip><p>

<sect><bf>strncmp</bf><label id="strncmp"><p><descrip>
<tag> Synopsis </tag> Compare the first few characters of two strings
<tag> Usage </tag> <tt>Integer_Type strncmp (String_Type a, String_Type b, Integer_Type n)</tt>
<tag> Description </tag>
  This function behaves like <tt>strcmp</tt> except that it compares only the
  first <tt>n</tt> characters in the strings <tt>a</tt> and <tt>b</tt>.  See
  the documentation for <tt>strcmp</tt> for information about the return
  value.
<tag> Example </tag>
  The expression
<tscreen><verb>
     strcmp ("apple", "appliance", 3);
</verb></tscreen>
  will return zero since the first three characters match.
<tag> See Also </tag> <tt>strcmp, strlen</tt>
</descrip><p>

<sect><bf>strreplace</bf><label id="strreplace"><p><descrip>
<tag> Synopsis </tag> Replace one or more substrings
<tag> Usage </tag> <tt>(new, n) = strreplace (a, b, c, max_n)</tt>
<tscreen><verb>
   String_Type a, b, c, rep;
   Int_Type n, max_n;
</verb></tscreen>
<tag> Description </tag>
  The <tt>strreplace</tt> function may be used to replace one or more
  occurances of <tt>b</tt> in <tt>a</tt> with <tt>c</tt>.  If the integer
  <tt>max_n</tt> is positive, then the first <tt>max_n</tt> occurances of
  <tt>b</tt> in <tt>a</tt> will be replaced.  Otherwise, if <tt>max_n</tt> is
  negative, then the last <tt>abs(max_n)</tt> occurances will be replaced.
  
  The function returns the resulting string and an integer indicating
  how many replacements were made.
<tag> Example </tag>
  The following function illustrates how <tt>strreplace</tt> may be used
  to remove all occurances of a specified substring
<tscreen><verb>
  define delete_substrings (a, b)
  {
     (a, ) = strreplace (a, b, "", strlen (a));
     return a;
  }
</verb></tscreen>
<tag> See Also </tag> <tt>is_substr, strsub, strtrim, strtrans, str_delete_chars</tt>
</descrip><p>

<sect><bf>strsub</bf><label id="strsub"><p><descrip>
<tag> Synopsis </tag> Replace a character with another in a string.
<tag> Usage </tag> <tt>String_Type strsub (String_Type s, Integer_Type pos, Integer_Type ch)</tt>
<tag> Description </tag>
  The <tt>strsub</tt> character may be used to substitute the character
  <tt>ch</tt> for the character at position <tt>pos</tt> of the string
  <tt>s</tt>.  The resulting string is returned.
<tag> Example </tag>
<tscreen><verb>
    define replace_spaces_with_comma (s)
    {
      variable n;
      while (n = is_substr (s, " "), n) s = strsub (s, n, ',');
      return s;
    }
</verb></tscreen>
  For uses such as this, the <tt>strtrans</tt> function is a better choice.
<tag> Notes </tag>
  The first character in the string <tt>s</tt> is specified by <tt>pos</tt>
  equal to 1.
<tag> See Also </tag> <tt>is_substr, strreplace, strlen</tt>
</descrip><p>

<sect><bf>strtok</bf><label id="strtok"><p><descrip>
<tag> Synopsis </tag> Extract tokens from a string
<tag> Usage </tag> <tt>String_Type[] strtok (String_Type str [,String_Type white])</tt>
<tag> Description </tag>
  <tt>strtok</tt> breaks the string <tt>str</tt> into a series of tokens and
  returns them as an array of strings.  If the second parameter
  <tt>white</tt> is present, then it specifies the set of characters that
  are to be regarded as whitespace when extracting the tokens, and may
  consist of the whitespace characters or a range of such characters.
  If the first character of <tt>white</tt> is <tt>'^'</tt>, then the
  whitespace characters consist of all characters except those in
  <tt>white</tt>. For example, if <tt>white</tt> is <tt>" \t\n,;."</tt>,
  then those characters specifiy the whitespace characters.  However,
  if <tt>white</tt> is given by <tt>"^a-zA-Z0-9_"</tt>, then any character
  is a whitespace character except those in the ranges <tt>a-z</tt>,
  <tt>A-Z</tt>, <tt>0-9</tt>, and the underscore character.
  
  If the second parameter is not present, then it defaults to 
  <tt>" \t\r\n\f"</tt>.
<tag> Example </tag>
  The following example may be used to count the words in a text file:
<tscreen><verb>
    define count_words (file)
    {
       variable fp, line, count;
       
       fp = fopen (file, "r");
       if (fp == NULL) return -1;
       
       count = 0;
       while (-1 != fgets (&amp;line, fp))
         {
           line = strtok (line, "^a-zA-Z");
           count += length (line);
         }
       () = fclose (fp);
       return count;
    }
</verb></tscreen>
<tag> See Also </tag> <tt>strchop, strcompress, extract_element, strjoin</tt>
</descrip><p>

<sect><bf>strtrans</bf><label id="strtrans"><p><descrip>
<tag> Synopsis </tag> Replace characters in a string
<tag> Usage </tag> <tt>String_Type strtrans (str, old_set, new_set)</tt>
<tscreen><verb>
   String_Type str, old_set, new_set;
</verb></tscreen>
<tag> Description </tag>
  The <tt>strtrans</tt> function may be used to replace all the characters
  from the set <tt>old_set</tt> with the corresponding characters from
  <tt>new_set</tt> in the string <tt>str</tt>.  If <tt>new_set</tt> is empty,
  then the characters in <tt>old_set</tt> will be removed from <tt>str</tt>.
  This function returns the result.
<tag> Example </tag>
<tscreen><verb>
    str = strtrans (str, "A-Z", "a-z");   % lower-case str
    str = strtrans (str, "^0-9", " ");    % Replace anything but 0-9 by space
</verb></tscreen>
<tag> See Also </tag> <tt>strreplace, strtrim, strup, strlow</tt>
</descrip><p>

<sect><bf>strtrim</bf><label id="strtrim"><p><descrip>
<tag> Synopsis </tag> Remove whitespace from the ends of a string
<tag> Usage </tag> <tt>String_Type strtrim (String_Type s [,String_Type w])</tt>
<tag> Description </tag>
  The <tt>strtrim</tt> function removes all leading and trailing whitespace
  characters from the string <tt>s</tt> and returns the result.  The
  optional second parameter specifies the set of whitespace
  characters.  If the argument is not present, then the set defaults
  to <tt>" \t\r\n"</tt>.
<tag> See Also </tag> <tt>strtrim_beg, strtrim_end, strcompress</tt>
</descrip><p>

<sect><bf>strtrim_beg</bf><label id="strtrim_beg"><p><descrip>
<tag> Synopsis </tag> Remove leading whitespace from a string
<tag> Usage </tag> <tt>String_Type strtrim_beg (String_Type s [,String_Type w])</tt>
<tag> Description </tag>
  The <tt>strtrim_beg</tt> function removes all leading whitespace
  characters from the string <tt>s</tt> and returns the result.  The
  optional second parameter specifies the set of whitespace
  characters.  If the argument is not present, then the set defaults
  to <tt>" \t\r\n"</tt>.
<tag> See Also </tag> <tt>strtrim, strtrim_end, strcompress</tt>
</descrip><p>

<sect><bf>strtrim_end</bf><label id="strtrim_end"><p><descrip>
<tag> Synopsis </tag> Remove trailing whitespace from a string
<tag> Usage </tag> <tt>String_Type strtrim_end (String_Type s [,String_Type w])</tt>
<tag> Description </tag>
  The <tt>strtrim_end</tt> function removes all trailing whitespace
  characters from the string <tt>s</tt> and returns the result.  The
  optional second parameter specifies the set of whitespace
  characters.  If the argument is not present, then the set defaults
  to <tt>" \t\r\n"</tt>.
<tag> See Also </tag> <tt>strtrim, strtrim_beg, strcompress</tt>
</descrip><p>

<sect><bf>strup</bf><label id="strup"><p><descrip>
<tag> Synopsis </tag> Convert a string to uppercase
<tag> Usage </tag> <tt>String_Type strup (String_Type s)</tt>
<tag> Description </tag>
  The <tt>strup</tt> function takes a string <tt>s</tt> and returns another
  string identical to <tt>s</tt> except that all lower case characters
  that comprise <tt>s</tt> will be converted to upper case.
<tag> Example </tag>
  The function
<tscreen><verb>
    define Strcmp (a, b)
    {
      return strcmp (strup (a), strup (b));
    }
</verb></tscreen>
  performs a case-insensitive comparison operation of two strings by
  converting them to upper case first.
<tag> See Also </tag> <tt>strlow, toupper, strcmp, strtrim, define_case, strtrans</tt>
</descrip><p>

<sect><bf>substr</bf><label id="substr"><p><descrip>
<tag> Synopsis </tag> Extract a substring from a string
<tag> Usage </tag> <tt>String_Type substr (String_Type s, Integer_Type n, Integer_Type len)</tt>
<tag> Description </tag>
  The <tt>substr</tt> function returns a substring with length <tt>len</tt>
  of the string <tt>s</tt> beginning at position <tt>n</tt>.  If <tt>len</tt> is
  <tt>-1</tt>, the entire length of the string <tt>s</tt> will be used for
  <tt>len</tt>.  The first character of <tt>s</tt> is given by <tt>n</tt> equal
  to 1.
<tag> Example </tag>
<tscreen><verb>
     substr ("To be or not to be", 7, 5);
</verb></tscreen>
  returns <tt>"or no"</tt>
<tag> Notes </tag>
  In many cases it is more convenient to use array indexing rather
  than the <tt>substr</tt> function.  In fact, <tt>substr(s,i+1,strlen(s))</tt> is
  equivalent to <tt>s[[i:]]</tt>.
<tag> See Also </tag> <tt>is_substr, strlen</tt>
</descrip><p>


<chapt>Functions that Manipulate Structures<p>
<sect><bf>_push_struct_field_values</bf><label id="_push_struct_field_values"><p><descrip>
<tag> Synopsis </tag> Push the values of a structure's fields onto the stack
<tag> Usage </tag> <tt>Integer_Type num = _push_struct_field_values (Struct_Type s)</tt>
<tag> Description </tag>
  The <tt>_push_struct_field_values</tt> function pushes the values of
  all the fields of a structure onto the stack, returning the
  number of items pushed.  The fields are pushed such that the last
  field of the structure is pushed first.
<tag> See Also </tag> <tt>get_struct_field_names, get_struct_field</tt>
</descrip><p>

<sect><bf>get_struct_field</bf><label id="get_struct_field"><p><descrip>
<tag> Synopsis </tag> Get the value associated with a structure field
<tag> Usage </tag> <tt>x = get_struct_field (Struct_Type s, String field_name)</tt>
<tag> Description </tag>
   The <tt>get_struct_field</tt> function gets the value of the field
   whose name is specified by <tt>field_name</tt> of the structure <tt>s</tt>.
<tag> Example </tag>
   The following example illustrates how this function may be used to 
   to print the value of a structure.
<tscreen><verb>
      define print_struct (s)
      {
         variable name;

         foreach (get_struct_field_names (s))
           {
             name = ();
             value = get_struct_field (s, name);
             vmessage ("s.%s = %s\n", name, string(value));
           }
      }
</verb></tscreen>
<tag> See Also </tag> <tt>set_struct_field, get_struct_field_names, array_info</tt>

</descrip><p>

<sect><bf>get_struct_field_names</bf><label id="get_struct_field_names"><p><descrip>
<tag> Synopsis </tag> Retrieve the field names associated with a structure
<tag> Usage </tag> <tt>String_Type[] = get_struct_field_names (Struct_Type s)</tt>
<tag> Description </tag>
   The <tt>get_struct_field_names</tt> function returns an array of
   strings whose elements specify the names of the fields of the
   struct <tt>s</tt>.
<tag> Example </tag>
   The following example illustrates how the
   <tt>get_struct_field_names</tt> function may be used to print the
   value of a structure.
<tscreen><verb>
      define print_struct (s)
      {
         variable name, value;

         foreach (get_struct_field_names (s))
           {
             name = ();
             value = get_struct_field (s, name);
             vmessage ("s.%s = %s\n", name, string (value));
           }
      }
</verb></tscreen>
<tag> See Also </tag> <tt>_push_struct_field_values, get_struct_field</tt>
</descrip><p>

<sect><bf>is_struct_type</bf><label id="is_struct_type"><p><descrip>
<tag> Synopsis </tag> Determine whether or not an object is a structure
<tag> Usage </tag> <tt>Integer_Type is_struct_type (X)</tt>
<tag> Description </tag>
  The <tt>is_struct_type</tt> function returns <tt>1</tt> if the the parameter
  refers to a structure or a user-defined type.  If the object is
  neither, <tt>0</tt> will be returned.
<tag> See Also </tag> <tt>typeof, _typeof</tt>
</descrip><p>

<sect><bf>set_struct_field</bf><label id="set_struct_field"><p><descrip>
<tag> Synopsis </tag> Set the value associated with a structure field
<tag> Usage </tag> <tt>set_struct_field (s, field_name, field_value)</tt>
<tscreen><verb>
   Struct_Type s;
   String_Type field_name;
   Generic_Type field_value;
</verb></tscreen>
<tag> Description </tag>
   The <tt>set_struct_field</tt> function sets the value of the field
   whose name is specified by <tt>field_name</tt> of the structure
   <tt>s</tt> to <tt>field_value</tt>.
<tag> See Also </tag> <tt>get_struct_field, get_struct_field_names, set_struct_fields, array_info</tt>
</descrip><p>

<sect><bf>set_struct_fields</bf><label id="set_struct_fields"><p><descrip>
<tag> Synopsis </tag> Set the fields of a structure
<tag> Usage </tag> <tt>set_struct_fields (Struct_Type s, ...)</tt>
<tag> Description </tag>
  The <tt>set_struct_fields</tt> function may be used to set zero or more
  fields of a structure.  The fields are set in the order in which
  they were created when the structure was defined.
<tag> Example </tag>
<tscreen><verb>
    variable s = struct { name, age, height };
    set_struct_fields (s, "Bill", 13, 64);
</verb></tscreen>
<tag> See Also </tag> <tt>set_struct_field, get_struct_field_names</tt>
</descrip><p>


<chapt>Informational Functions<p>
<sect><bf>_NARGS</bf><label id="_NARGS"><p><descrip>
<tag> Synopsis </tag> The number of parameters passed to a function
<tag> Usage </tag> <tt>Integer_Type _NARGS</tt>
   The value of the <tt>_NARGS</tt> variable represents the number of
   arguments passed to the function.  This variable is local to each
   function.
<tag> Example </tag>
   This example uses the <tt>_NARGS</tt> variable to print the list of
   values passed to the function:
<tscreen><verb>
     define print_values ()
     {
        variable arg;
        
        if (_NARGS == 0)
          {
             message ("Nothing to print");
             return;
          }
        foreach (__pop_args (_NARGS))
          {
             arg = ();
             vmessage ("Argument value is: %S", arg.value);
          }
     }
</verb></tscreen>
<tag> See Also </tag> <tt>__pop_args, __push_args, typeof</tt>
</descrip><p>

<sect><bf>__get_defined_symbols</bf><label id="__get_defined_symbols"><p><descrip>
<tag> Synopsis </tag> Get the symbols defined by the preprocessor
<tag> Usage </tag> <tt>Integer_Type __get_defined_symbols ()</tt>
<tag> Description </tag>
  The <tt>__get_defined_symbols</tt> functions is used to get the list of
  all the symbols defined by the <bf>S-lang</bf> preprocessor.  It pushes each
  of the symbols on the stack followed by the number of items pushed.
<tag> See Also </tag> <tt>is_defined, _apropos, _get_namespaces</tt>
</descrip><p>

<sect><bf>__is_initialized</bf><label id="__is_initialized"><p><descrip>
<tag> Synopsis </tag> Determine whether or not a variable has a value
<tag> Usage </tag> <tt>Integer_Type __is_initialized (Ref_Type r)</tt>
<tag> Description </tag>
   This function returns non-zero of the object referenced by <tt>r</tt>
   is initialized, i.e., whether it has a value.  It returns <tt>0</tt> if the
   referenced object has not been initialized.
<tag> Example </tag>
   For example, the function:
<tscreen><verb>
    define zero ()
    {
       variable f;
       return __is_initialized (&amp;f);
    }
</verb></tscreen>
  will always return zero, but
<tscreen><verb>
    define one ()
    {
       variable f = 0;
       return __is_initialized (&amp;f);
    }
</verb></tscreen>
  will return one.
<tag> Notes </tag>
  It is easy to see why a reference to the variable must be passed to
  <tt>__is_initialized</tt> and not the variable itself; otherwise, the
  value of the variable would be passed and the variable may have no
  value if it was not initialized.
<tag> See Also </tag> <tt>__get_reference, __uninitialize, is_defined, typeof, eval</tt>
</descrip><p>

<sect><bf>_apropos</bf><label id="_apropos"><p><descrip>
<tag> Synopsis </tag> Generate a list of functions and variables
<tag> Usage </tag> <tt>Array_Type _apropos (String_Type ns, String_Type s, Integer_Type flags)</tt>
<tag> Description </tag>
  The <tt>_apropos</tt> function may be used to get a list of all defined
  objects in the namespace <tt>ns</tt> whose name matches the regular
  expression <tt>s</tt> and whose type matches those specified by
  <tt>flags</tt>.  It returns an array of strings representing the
  matches. 

  The second parameter <tt>flags</tt> is a bit mapped value whose bits
  are defined according to the following table
<tscreen><verb>
     1          Intrinsic Function
     2          User-defined Function
     4          Intrinsic Variable
     8          User-defined Variable
</verb></tscreen>
<tag> Example </tag>
<tscreen><verb>
    define apropos (s)
    {
      variable n, name, a;
      a = _apropos ("Global", s, 0xF);
      
      vmessage ("Found %d matches:", length (a));
      foreach (a)
        {
           name = ();
           message (name);
        }
    }
</verb></tscreen>
  prints a list of all matches.
<tag> Notes </tag>
  If the namespace specifier <tt>ns</tt> is the empty string <tt>""</tt>,
  then the namespace will default to the static namespace of the
  current compilation unit.
<tag> See Also </tag> <tt>is_defined, sprintf, _get_namespaces</tt>
</descrip><p>

<sect><bf>_function_name</bf><label id="_function_name"><p><descrip>
<tag> Synopsis </tag> Returns the name of the currently executing function
<tag> Usage </tag> <tt>String_Type _function_name ()</tt>
<tag> Description </tag>
  This function returns the name of the currently executing function.
  If called from top-level, it returns the empty string.
<tag> See Also </tag> <tt>_trace_function, is_defined</tt>
</descrip><p>

<sect><bf>_get_namespaces</bf><label id="_get_namespaces"><p><descrip>
<tag> Synopsis </tag> Returns a list of namespace names
<tag> Usage </tag> <tt>String_Type[] _get_namespaces ()</tt>
<tag> Description </tag>
  This function returns a string array containing the names of the
  currently defined namespaces.
<tag> See Also </tag> <tt>_apropos, use_namespace, implements, __get_defined_symbols</tt>
</descrip><p>

<sect><bf>_slang_doc_dir</bf><label id="_slang_doc_dir"><p><descrip>
<tag> Synopsis </tag> Installed documentation directory
<tag> Usage </tag> <tt>String_Type _slang_doc_dir;</tt>
<tag> Description </tag>
   The <tt>_slang_doc_dir</tt> variable is a read-only whose value
   specifies the installation location of the <bf>S-lang</bf> documentation.
<tag> See Also </tag> <tt>get_doc_string_from_file</tt>
</descrip><p>

<sect><bf>_slang_version</bf><label id="_slang_version"><p><descrip>
<tag> Synopsis </tag> The S-Lang library version number
<tag> Usage </tag> <tt>Integer_Type _slang_version</tt>
<tag> Description </tag>
   The <tt>_slang_version</tt> variable is read-only and and whose
   value represents the number of the <bf>S-lang</bf> library.
<tag> See Also </tag> <tt>_slang_version_string</tt>
</descrip><p>

<sect><bf>_slang_version_string</bf><label id="_slang_version_string"><p><descrip>
<tag> Synopsis </tag> The S-Lang library version number as a string
<tag> Usage </tag> <tt>String_Type _slang_version_string</tt>
<tag> Description </tag>
   The <tt>_slang_version_string</tt> variable is read-only and whose
   value represents the version number of the <bf>S-lang</bf> library.
<tag> See Also </tag> <tt>_slang_version</tt>
</descrip><p>

<sect><bf>get_doc_string_from_file</bf><label id="get_doc_string_from_file"><p><descrip>
<tag> Synopsis </tag> Read documentation from a file
<tag> Usage </tag> <tt>String_Type get_doc_string_from_file (String_Type f, String_Type t)</tt>
<tag> Description </tag>
  <tt>get_doc_string_from_file</tt> opens the documentation file <tt>f</tt>
  and searches it for topic <tt>t</tt>.  It returns the documentation for
  <tt>t</tt> upon success, otherwise it returns <tt>NULL</tt> upon error.
  It will fail if <tt>f</tt> could not be opened or does not contain
  documentation for the topic.
<tag> See Also </tag> <tt>stat_file</tt>
<tag> See Also </tag> <tt>_slang_doc_dir</tt>
</descrip><p>

<sect><bf>is_defined</bf><label id="is_defined"><p><descrip>
<tag> Synopsis </tag> Indicate whether a variable or function defined.
<tag> Usage </tag> <tt>Integer_Type is_defined (String_Type obj)</tt>
<tag> Description </tag>
   This function is used to determine whether or not a function or
   variable whose name is <tt>obj</tt> has been defined.  If <tt>obj</tt> is not
   defined, the function returns 0.  Otherwise, it returns a non-zero
   value that defpends on the type of object <tt>obj</tt> represents.
   Specifically, it returns one of the following values:
<tscreen><verb>
     +1 if an intrinsic function
     +2 if user defined function
     -1 if intrinsic variable
     -2 if user defined variable
      0 if undefined
</verb></tscreen>
<tag> Example </tag>
    For example, consider the function:
<tscreen><verb>
    define runhooks (hook)
    {
       if (2 == is_defined(hook)) eval(hook);
    }
</verb></tscreen>
    This function could be called from another <bf>S-lang</bf> function to
    allow customization of that function, e.g., if the function
    represents a mode, the hook could be called to setup keybindings
    for the mode.
<tag> See Also </tag> <tt>typeof, eval, autoload, __get_reference, __is_initialized</tt>
</descrip><p>


<chapt>Mathematical Functions<p>
<sect><bf>Conj</bf><label id="Conj"><p><descrip>
<tag> Synopsis </tag> Compute the complex conjugate of a number
<tag> Usage </tag> <tt>z1 = Conj (z)</tt>
<tag> Description </tag>
  The <tt>Conj</tt> function returns the complex conjugate of a number.
  If its argument is an array, the <tt>Conj</tt> function will be applied to each
  element and the result returned as an array.
<tag> See Also </tag> <tt>Real, Imag, abs</tt>
</descrip><p>

<sect><bf>Imag</bf><label id="Imag"><p><descrip>
<tag> Synopsis </tag> Compute the imaginary part of a number
<tag> Usage </tag> <tt>i = Imag (z)</tt>
<tag> Description </tag>
  The <tt>Imag</tt> function returns the imaginary part of a number.
  If its argument is an array, the <tt>Imag</tt> function will be applied to each
  element and the result returned as an array.
<tag> See Also </tag> <tt>Real, Conj, abs</tt>
</descrip><p>

<sect><bf>Real</bf><label id="Real"><p><descrip>
<tag> Synopsis </tag> Compute the real part of a number
<tag> Usage </tag> <tt>r = Real (z)</tt>
<tag> Description </tag>
  The <tt>Real</tt> function returns the real part of a number. If its
  argument is an array, the <tt>Real</tt> function will be applied to
  each element and the result returned as an array.
<tag> See Also </tag> <tt>Imag, Conj, abs</tt>
</descrip><p>

<sect><bf>abs</bf><label id="abs"><p><descrip>
<tag> Synopsis </tag> Compute the absolute value of a number
<tag> Usage </tag> <tt>y = abs(x)</tt>
<tag> Description </tag>
  The <tt>abs</tt> function returns the absolute value of an arithmetic
  type.  If its argument is a complex number (<tt>Complex_Type</tt>),
  then it returns the modulus.  If the argument is an array, a new
  array will be created whose elements are obtained from the original
  array by using the <tt>abs</tt> function.
<tag> See Also </tag> <tt>sign, sqr</tt>
</descrip><p>

<sect><bf>acos</bf><label id="acos"><p><descrip>
<tag> Synopsis </tag> Compute the arc-cosine of an number
<tag> Usage </tag> <tt>y = acos (x)</tt>
<tag> Description </tag>
  The <tt>acos</tt> function computes the arc-cosine of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>acos</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>acosh</bf><label id="acosh"><p><descrip>
<tag> Synopsis </tag> Compute the inverse cosh of an number
<tag> Usage </tag> <tt>y = acosh (x)</tt>
<tag> Description </tag>
  The <tt>acosh</tt> function computes the inverse cosh of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>acosh</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>asin</bf><label id="asin"><p><descrip>
<tag> Synopsis </tag> Compute the arc-sine of an number
<tag> Usage </tag> <tt>y = asin (x)</tt>
<tag> Description </tag>
  The <tt>asin</tt> function computes the arc-sine of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>asin</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>asinh</bf><label id="asinh"><p><descrip>
<tag> Synopsis </tag> Compute the inverse-sinh of an number
<tag> Usage </tag> <tt>y = asinh (x)</tt>
<tag> Description </tag>
  The <tt>asinh</tt> function computes the inverse-sinh of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>asinh</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>atan</bf><label id="atan"><p><descrip>
<tag> Synopsis </tag> Compute the arc-tangent of an number
<tag> Usage </tag> <tt>y = atan (x)</tt>
<tag> Description </tag>
  The <tt>atan</tt> function computes the arc-tangent of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>atan</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>atanh</bf><label id="atanh"><p><descrip>
<tag> Synopsis </tag> Compute the inverse-tanh of an number
<tag> Usage </tag> <tt>y = atanh (x)</tt>
<tag> Description </tag>
  The <tt>atanh</tt> function computes the inverse-tanh of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>atanh</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>cos</bf><label id="cos"><p><descrip>
<tag> Synopsis </tag> Compute the cosine of an number
<tag> Usage </tag> <tt>y = cos (x)</tt>
<tag> Description </tag>
  The <tt>cos</tt> function computes the cosine of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>cos</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>cosh</bf><label id="cosh"><p><descrip>
<tag> Synopsis </tag> Compute the hyperbolic cosine of an number
<tag> Usage </tag> <tt>y = cosh (x)</tt>
<tag> Description </tag>
  The <tt>cosh</tt> function computes the hyperbolic cosine of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>cosh</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>exp</bf><label id="exp"><p><descrip>
<tag> Synopsis </tag> Compute the exponential of an number
<tag> Usage </tag> <tt>y = exp (x)</tt>
<tag> Description </tag>
  The <tt>exp</tt> function computes the exponential of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>exp</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>log</bf><label id="log"><p><descrip>
<tag> Synopsis </tag> Compute the logarithm of an number
<tag> Usage </tag> <tt>y = log (x)</tt>
<tag> Description </tag>
  The <tt>log</tt> function computes the logarithm of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>log</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>log10</bf><label id="log10"><p><descrip>
<tag> Synopsis </tag> Compute the base-10 logarithm of an number
<tag> Usage </tag> <tt>y = log10 (x)</tt>
<tag> Description </tag>
  The <tt>log10</tt> function computes the base-10 logarithm of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>log10</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>mul2</bf><label id="mul2"><p><descrip>
<tag> Synopsis </tag> Multiply a number by 2
<tag> Usage </tag> <tt>y = mul2(x)</tt>
<tag> Description </tag>
  The <tt>mul2</tt> function multiplies an arithmetic type by two and
  returns the result.  If its argument is an array, a new array will
  be created whose elements are obtained from the original array by
  using the <tt>mul2</tt> function.
<tag> See Also </tag> <tt>sqr, abs</tt>
</descrip><p>

<sect><bf>polynom</bf><label id="polynom"><p><descrip>
<tag> Synopsis </tag> Evaluate a polynomial
<tag> Usage </tag> <tt>Double_Type polynom(Double_Type a, b, ...c, Integer_Type n, Double_Type x)</tt>
<tag> Description </tag>
  The <tt>polynom</tt> function returns the value of the polynomial expression:
<tscreen><verb>
     ax^n + bx^(n - 1) + ... c
</verb></tscreen>
<tag> Notes </tag>
  The <tt>polynom</tt> function should be extended to work with complex
  and array data types.  The current implementation is limited to
  <tt>Double_Type</tt> quantities.
<tag> See Also </tag> <tt>exp</tt>
</descrip><p>

<sect><bf>set_float_format</bf><label id="set_float_format"><p><descrip>
<tag> Synopsis </tag> Set the format for printing floating point values.
<tag> Usage </tag> <tt>set_float_format (String_Type fmt)</tt>
<tag> Description </tag>
  The <tt>set_float_format</tt> function is used to set the floating
  point format to be used when floating point numbers are printed.
  The routines that use this are the traceback routines and the
  <tt>string</tt> function. The default value is <tt>"%f"</tt>
<tag> Example </tag>
<tscreen><verb>
     s = string (PI);                %  --&gt; s = "3.14159"
     set_float_format ("%16.10f");
     s = string (PI);                %  --&gt; s = "3.1415926536"
     set_float_format ("%10.6e");
     s = string (PI);                %  --&gt; s = "3.141593e+00"
</verb></tscreen>
<tag> See Also </tag> <tt>string, sprintf, double</tt>
</descrip><p>

<sect><bf>sign</bf><label id="sign"><p><descrip>
<tag> Synopsis </tag> Compute the sign of a number
<tag> Usage </tag> <tt>y = sign(x)</tt>
<tag> Description </tag>
  The <tt>sign</tt> function returns the sign of an arithmetic type.  If
  its argument is a complex number (<tt>Complex_Type</tt>), it returns
  the sign of the imaginary part of the number. If the argument is an
  array, a new array will be created whose elements are obtained from
  the original array by using the <tt>sign</tt> function.
  
  When applied to a real number or an integer, the <tt>sign</tt> function
  returns <tt>-1</tt>, <tt>0</tt>, or <tt>+1</tt> according to whether the number is
  less than zero, equal to zero, or greater than zero, respectively.
<tag> See Also </tag> <tt>abs</tt>
</descrip><p>

<sect><bf>sin</bf><label id="sin"><p><descrip>
<tag> Synopsis </tag> Compute the sine of an number
<tag> Usage </tag> <tt>y = sin (x)</tt>
<tag> Description </tag>
  The <tt>sin</tt> function computes the sine of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>sin</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>sinh</bf><label id="sinh"><p><descrip>
<tag> Synopsis </tag> Compute the hyperbolic sine of an number
<tag> Usage </tag> <tt>y = sinh (x)</tt>
<tag> Description </tag>
  The <tt>sinh</tt> function computes the hyperbolic sine of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>sinh</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>sqr</bf><label id="sqr"><p><descrip>
<tag> Synopsis </tag> Compute the square of a number
<tag> Usage </tag> <tt>y = sqr(x)</tt>
<tag> Description </tag>
  The <tt>sqr</tt> function returns the square of an arithmetic type.  If its
  argument is a complex number (<tt>Complex_Type</tt>), then it returns
  the square of the modulus.  If the argument is an array, a new array
  will be created whose elements are obtained from the original array
  by using the <tt>sqr</tt> function.
<tag> See Also </tag> <tt>abs, mul2</tt>
</descrip><p>

<sect><bf>sqrt</bf><label id="sqrt"><p><descrip>
<tag> Synopsis </tag> Compute the square root of an number
<tag> Usage </tag> <tt>y = sqrt (x)</tt>
<tag> Description </tag>
  The <tt>sqrt</tt> function computes the square root of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>sqrt</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>sqr, cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>tan</bf><label id="tan"><p><descrip>
<tag> Synopsis </tag> Compute the tangent of an number
<tag> Usage </tag> <tt>y = tan (x)</tt>
<tag> Description </tag>
  The <tt>tan</tt> function computes the tangent of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>tan</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>

<sect><bf>tanh</bf><label id="tanh"><p><descrip>
<tag> Synopsis </tag> Compute the hyperbolic tangent of an number
<tag> Usage </tag> <tt>y = tanh (x)</tt>
<tag> Description </tag>
  The <tt>tanh</tt> function computes the hyperbolic tangent of a number and
  returns the result as an array.  If its argument is an array, the
  <tt>tanh</tt> function will be applied to each element and the result returned
  as an array.
<tag> See Also </tag> <tt>cos, atan, acosh, cosh</tt>
</descrip><p>


<chapt>Message and Error Functions<p>
<sect><bf>error</bf><label id="error"><p><descrip>
<tag> Synopsis </tag> Generate an error condition
<tag> Usage </tag> <tt>error (String_Type msg</tt>
<tag> Description </tag>
  The <tt>error</tt> function generates a <bf>S-lang</bf> error condition causing
  the interpreter to start unwinding to top-level.  It takes a single
  string parameter which is displayed on the stderr output device.
  The error condition may be cleared via an <tt>ERROR_BLOCK</tt> with the
  <tt>_clear_error</tt> function.  Consult <bf>A Guide to the S-Lang Language</bf> for more
  information.
<tag> Example </tag>
<tscreen><verb>
    define add_txt_extension (file)
    {
       if (typeof (file) != String_Type)
         error ("add_extension: parameter must be a string");
       file += ".txt";
       return file;
    }
</verb></tscreen>
<tag> See Also </tag> <tt>verror, _clear_error, message</tt>
</descrip><p>

<sect><bf>message</bf><label id="message"><p><descrip>
<tag> Synopsis </tag> Print a string onto the message device
<tag> Usage </tag> <tt>message (String_Type s</tt>
<tag> Description </tag>
  The <tt>message</tt> function will print the string specified by
  <tt>s</tt> onto the message device.
<tag> Example </tag>
<tscreen><verb>
     define print_current_time ()
     {
       message (time ());
     }
</verb></tscreen>
<tag> Notes </tag>
  The message device will depend upon the application.  For example,
  the output message device for the <tt>jed</tt> editor correspond to the
  line at the bottom of the display window.  The default message
  device is the standard output device.
<tag> See Also </tag> <tt>vmessage, sprintf, error</tt>
</descrip><p>

<sect><bf>usage</bf><label id="usage"><p><descrip>
<tag> Synopsis </tag> Generate a usage error
<tag> Usage </tag> <tt>usage (String_Type msg)</tt>
<tag> Description </tag>
  The <tt>usage</tt> function generates a usage exception and displays
  <tt>msg</tt> to the message device.
<tag> Example </tag>
  Suppose that some function <tt>plot</tt> plots an array of <tt>x</tt> and
  <tt>y</tt> values.  The such a function could be written to issue a
  usage message if the wrong number of arguments were passed:
<tscreen><verb>
    define plot ()
    { 
       variable x, y;

       if (_NARGS != 2)
         usage ("plot (x, y)");
       
       (x, y) = ();
       % Now do the hard part
          .
	  .
    }
</verb></tscreen>
<tag> See Also </tag> <tt>error, message</tt>
</descrip><p>

<sect><bf>verror</bf><label id="verror"><p><descrip>
<tag> Synopsis </tag> Generate an error condition
<tag> Usage </tag> <tt>verror (String_Type fmt, ...)</tt>
<tag> Description </tag>
  The <tt>verror</tt> function performs the same role as the <tt>error</tt>
  function.  The only difference is that instead of a single string
  argument, <tt>verror</tt> takes a sprintf style argument list.
<tag> Example </tag>
<tscreen><verb>
    define open_file (file)
    {
       variable fp;

       fp = fopen (file, "r");
       if (fp == NULL) verror ("Unable to open %s", file);
       return fp;
    }
</verb></tscreen>
<tag> Notes </tag>
  In the current implementation, strictly speaking, the <tt>verror</tt>
  function is not an intrinsic function.  Rather it is a predefined
  <bf>S-lang</bf> function using a combination of <tt>Sprintf</tt> and
  <tt>error</tt>.
<tag> See Also </tag> <tt>error, Sprintf, vmessage</tt>
</descrip><p>

<sect><bf>vmessage</bf><label id="vmessage"><p><descrip>
<tag> Synopsis </tag> Print a formatted string onto the message device
<tag> Usage </tag> <tt>vmessage (String_Type fmt, ...)</tt>
<tag> Description </tag>
  The <tt>vmessage</tt> function formats a sprintf style argument list
  and displays the resulting string onto the message device.
<tag> Notes </tag>
  In the current implementation, strictly speaking, the <tt>vmessage</tt>
  function is not an intrinsic function.  Rather it is a predefined
  <bf>S-lang</bf> function using a combination of <tt>Sprintf</tt> and
  <tt>message</tt>.
<tag> See Also </tag> <tt>message, Sprintf, verror</tt>
</descrip><p>


<chapt>Time and Date Functions<p>
<sect><bf>_time</bf><label id="_time"><p><descrip>
<tag> Synopsis </tag> Get the current time in seconds
<tag> Usage </tag> <tt>ULong_Type _time ()</tt>
<tag> Description </tag>
  The <tt>_time</tt> function returns the number of elapsed seconds since
  00:00:00 GMT, January 1, 1970.  The <tt>ctime</tt> function may be used
  to convert this into a string representation.
<tag> See Also </tag> <tt>ctime, time, localtime, gmtime</tt>
</descrip><p>

<sect><bf>ctime</bf><label id="ctime"><p><descrip>
<tag> Synopsis </tag> Convert a calendar time to a string
<tag> Usage </tag> <tt>String_Type ctime(ULong_Type secs)</tt>
<tag> Description </tag>
  This function returns a string representation of the time as given
  by <tt>secs</tt> seconds since 1970.
<tag> See Also </tag> <tt>time, _time, localtime, gmtime</tt>
</descrip><p>

<sect><bf>gmtime</bf><label id="gmtime"><p><descrip>
<tag> Synopsis </tag> Break down a time in seconds to GMT timezone
<tag> Usage </tag> <tt>Struct_Type gmtime (Long_Type secs)</tt>
<tag> Description </tag>
   The <tt>gmtime</tt> function is exactly like <tt>localtime</tt> except
   that the values in the structure it returns are with respect to GMT
   instead of the local timezone.  See the documentation for
   <tt>localtime</tt> for more information.
<tag> Notes </tag>
   On systems that do not support the <tt>gmtime</tt> C library function,
   this function is the same as <tt>localtime</tt>.
<tag> See Also </tag> <tt>localtime, _time</tt>
</descrip><p>

<sect><bf>localtime</bf><label id="localtime"><p><descrip>
<tag> Synopsis </tag> Break down a time in seconds to local timezone
<tag> Usage </tag> <tt>Struct_Type localtime (Long_Type secs)</tt>
<tag> Description </tag>
   The <tt>localtime</tt> function takes a parameter <tt>secs</tt>
   representing the number of seconds since 00:00:00, January 1 1970
   UTC and returns a structure containing information about <tt>secs</tt>
   in the local timezone.  The structure contains the following
   <tt>Int_Type</tt> fields:

   <tt>tm_sec</tt> The number of seconds after the minute, normally
      in the range 0 to 59, but can be up to 61 to allow for
      leap seconds.

   <tt>tm_min</tt> The number of minutes after the hour, in the
      range 0 to 59.

   <tt>tm_hour</tt> The number of hours past midnight, in the range
      0 to 23.

   <tt>tm_mday</tt> The day of the month, in the range 1 to 31.

   <tt>tm_mon</tt> The number of months since January, in the range
      0 to 11.

   <tt>tm_year</tt> The number of years since 1900.

   <tt>tm_wday</tt> The number of days since Sunday, in the range 0
      to 6.

   <tt>tm_yday</tt> The number of days since January 1, in the
      range 0 to 365.

   <tt>tm_isdst</tt> A flag that indicates whether daylight saving
      time is in effect at the time described.  The value is
      positive if daylight saving time is in effect, zero if it
      is not, and negative if the information is not available.
<tag> See Also </tag> <tt>gmtime, _time, ctime</tt>
</descrip><p>

<sect><bf>tic</bf><label id="tic"><p><descrip>
<tag> Synopsis </tag> Start timing
<tag> Usage </tag> <tt>void tic ()</tt>
<tag> Description </tag>
  The <tt>tic</tt> function restarts the internal clock used for timing
  the execution of commands.  To get the elapsed time of the clock,
  use the <tt>toc</tt> function.
<tag> See Also </tag> <tt>toc, times</tt>
</descrip><p>

<sect><bf>time</bf><label id="time"><p><descrip>
<tag> Synopsis </tag> Return the current data and time as a string
<tag> Usage </tag> <tt>String_Type time ()</tt>
<tag> Description </tag>
  This function returns the current time as a string of the form:
<tscreen><verb>
    Sun Apr 21 13:34:17 1996
</verb></tscreen>
<tag> See Also </tag> <tt>ctime, message, substr</tt>
</descrip><p>

<sect><bf>times</bf><label id="times"><p><descrip>
<tag> Synopsis </tag> Get process times
<tag> Usage </tag> <tt>Struct_Type times ()</tt>
<tag> Description </tag>
  The <tt>times</tt> function returns a structure containing the
  following fields:
<tscreen><verb>
    tms_utime     (user time)
    tms_stime     (system time)
    tms_cutime    (user time of child processes)
    tms_cstime    (system time of child processes)
</verb></tscreen>
<tag> Notes </tag>
  Not all systems support this function.
<tag> See Also </tag> <tt>tic, toc, _times</tt>
</descrip><p>

<sect><bf>toc</bf><label id="toc"><p><descrip>
<tag> Synopsis </tag> Get elapsed CPU time
<tag> Usage </tag> <tt>Double_Type toc ()</tt>
<tag> Description </tag>
  The <tt>toc</tt> function returns the elapsed CPU time in seconds since
  the last call to <tt>tic</tt>.  The CPU time is the amount of time the
  CPU spent running the code of the current process.
<tag> Example </tag>
  The <tt>tic</tt> and <tt>toc</tt> functions are ideal for timing the
  execution of the interpreter:
<tscreen><verb>
     variable a = "hello", b = "world", c, n = 100000, t;
     
     tic ();  loop (n) c = a + b; t = toc ();
     vmessage ("a+b took %f seconds\n", t);
     tic ();  loop (n) c = strcat(a,b); t = toc ();
     vmessage ("strcat took %f seconds\n", t);
</verb></tscreen>
<tag> Notes </tag>
  This function may not be available on all systems.

  The implementation of this function is based upon the <tt>times</tt>
  system call.  The precision of the clock is system dependent.
<tag> See Also </tag> <tt>tic, times, _time</tt>
</descrip><p>


<chapt>Data-Type Conversion Functions<p>
<sect><bf>_slang_guess_type</bf><label id="_slang_guess_type"><p><descrip>
<tag> Synopsis </tag> Guess the data type that a string represents.
<tag> Usage </tag> <tt>DataType_Type _slang_guess_type (String_Type s)</tt>
<tag> Description </tag>
  This function tries to determine whether its argument <tt>s</tt> represents
  an integer or a floating point number.  If it appears to be neither,
  then a string is assumed.  It returns one of three values depending on
  the format of the string <tt>s</tt>:
<tscreen><verb>
    Integer_Type     :   If it appears to be an integer
    Double_Type      :   If it appears to be a double
    String_Type      :   Anything else.
</verb></tscreen>
  For example, <tt>_slang_guess_type("1e2")</tt> returns
  <tt>Double_Type</tt> but <tt>_slang_guess_type("e12")</tt> returns
  <tt>String_Type</tt>.
<tag> See Also </tag> <tt>integer, string, double</tt>
</descrip><p>

<sect><bf>_typeof</bf><label id="_typeof"><p><descrip>
<tag> Synopsis </tag> Get the data type of an object
<tag> Usage </tag> <tt>DataType_Type _typeof (x)</tt>
<tag> Description </tag>
  This function is similar to the <tt>typeof</tt> function except in the
  case of arrays.  If the object <tt>x</tt> is an array, then the data
  type of the array will be returned. otherwise <tt>_typeof</tt> returns
  the data type of <tt>x</tt>. 
<tag> Example </tag>
<tscreen><verb>
  if (Integer_Type == _typeof (x)) 
    message ("x is an integer or an integer array");
</verb></tscreen>
<tag> See Also </tag> <tt>typeof, array_info, _slang_guess_type, typecast</tt>
</descrip><p>

<sect><bf>atof</bf><label id="atof"><p><descrip>
<tag> Synopsis </tag> Convert a string to a double precision number
<tag> Usage </tag> <tt>Double_Type atof (String_Type s)</tt>
<tag> Description </tag>
  This function converts a string <tt>s</tt> to a double precision value
  and returns the result.  It performs no error checking on the format
  of the string.  The function <tt>_slang_guess_type</tt> may be used to
  check the syntax of the string.
<tag> Example </tag>
<tscreen><verb>
     define error_checked_atof (s)
     {
        switch (_slang_guess_type (s))
        {
           case Double_Type:
             return atof (s);
        }
        {
           case Integer_Type:
             return double (integer (s));
        }

        verror ("%s is is not a double", s);
    }
</verb></tscreen>
<tag> See Also </tag> <tt>typecast, double, _slang_guess_type</tt>
</descrip><p>

<sect><bf>char</bf><label id="char"><p><descrip>
<tag> Synopsis </tag> Convert an ascii value into a string
<tag> Usage </tag> <tt>String_Type char (Integer_Type c)</tt>
<tag> Description </tag>
  The <tt>char</tt> function converts an integer ascii value <tt>c</tt> to a string
  of unit length such that the first character of the string is <tt>c</tt>.
  For example, <tt>char('a')</tt> returns the string <tt>"a"</tt>.
<tag> See Also </tag> <tt>integer, string, typedef</tt>
</descrip><p>

<sect><bf>define_case</bf><label id="define_case"><p><descrip>
<tag> Synopsis </tag> Define upper-lower case conversion.
<tag> Usage </tag> <tt>define_case (Integer_Type ch_up, Integer_Type ch_low);</tt>
<tag> Description </tag>
  This function defines an upper and lowercase relationship between two
  characters specified by the arguments.  This relationship is used by
  routines which perform uppercase and lowercase conversions.
  The first integer <tt>ch_up</tt> is the ascii value of the uppercase character
  and the second parameter <tt>ch_low</tt> is the ascii value of its
  lowercase counterpart.
<tag> See Also </tag> <tt>strlow, strup</tt>
</descrip><p>

<sect><bf>double</bf><label id="double"><p><descrip>
<tag> Synopsis </tag> Convert an object to double precision
<tag> Usage </tag> <tt>result = double (x)</tt>
<tag> Description </tag>
  The <tt>double</tt> function typecasts an object <tt>x</tt> to double
  precision.  For example, if <tt>x</tt> is an array of integers, an
  array of double types will be returned.  If an object cannot be
  converted to <tt>Double_Type</tt>, a type-mismatch error will result.
<tag> Notes </tag>
  The <tt>double</tt> function is equivalent to the typecast operation
<tscreen><verb>
     typecast (x, Double_Type)
</verb></tscreen>
  To convert a string to a double precision number, use <tt>atoi</tt>
  function.
<tag> See Also </tag> <tt>typecast, atoi, int</tt>
</descrip><p>

<sect><bf>int</bf><label id="int"><p><descrip>
<tag> Synopsis </tag> Typecast an object to an integer
<tag> Usage </tag> <tt>int (s)</tt>
<tag> Description </tag>
  This function performs a typecast of <tt>s</tt> from its data type to
  an object of <tt>Integer_Type</tt>.  If <tt>s</tt> is a string, it returns
  returns the ascii value value of the first character of the string
  <tt>s</tt>.  If <tt>s</tt> is <tt>Double_Type</tt>, <tt>int</tt> truncates the
  number to an integer and returns it.
<tag> Example </tag>
  <tt>int</tt> can be used to convert single character strings to
  integers.  As an example, the intrinsic function <tt>isdigit</tt> may
  be defined as
<tscreen><verb>
    define isdigit (s)
    {
      if ((int (s) &gt;= '0') and (int (s) &lt;= '9')) return 1;
      return 0;
    }
</verb></tscreen>
<tag> Notes </tag>
  This function is equalent to <tt>typecast (s, Integer_Type)</tt>;
<tag> See Also </tag> <tt>typecast, double, integer, char, isdigit</tt>
</descrip><p>

<sect><bf>integer</bf><label id="integer"><p><descrip>
<tag> Synopsis </tag> Convert a string to an integer
<tag> Usage </tag> <tt>Integer_Type integer (String_Type s)</tt>
<tag> Description </tag>
  The <tt>integer</tt> function converts a string representation of an
  integer back to an integer.  If the string does not form a valid
  integer, a type-mismatch error will be generated.
<tag> Example </tag>
  <tt>integer ("1234")</tt> returns the integer value <tt>1234</tt>.
<tag> Notes </tag>
  This function operates only on strings and is not the same as the
  more general <tt>typecast</tt> operator.
<tag> See Also </tag> <tt>typecast, _slang_guess_type, string, sprintf, char</tt>
</descrip><p>

<sect><bf>isdigit</bf><label id="isdigit"><p><descrip>
<tag> Synopsis </tag> Tests for a decimal digit character
<tag> Usage </tag> <tt>Integer_Type isdigit (String_Type s)</tt>
<tag> Description </tag>
  This function returns a non-zero value if the first character in the
  string <tt>s</tt> is a digit; otherwise, it returns zero.
<tag> Example </tag>
  A simple, user defined implementation of <tt>isdigit</tt> is
<tscreen><verb>
    define isdigit (s)
    {
       return ((s[0] &lt;= '9') and (s[0]  &gt;= '0'));
    }
</verb></tscreen>
  However, the intrinsic function <tt>isdigit</tt> executes many times faster
  than the equivalent representation defined above.
<tag> Notes </tag>
  Unlike the C function with the same name, the <bf>S-lang</bf> function takes
  a string argument.
<tag> See Also </tag> <tt>int, integer</tt>
</descrip><p>

<sect><bf>string</bf><label id="string"><p><descrip>
<tag> Synopsis </tag> Convert an object to a string representation.
<tag> Usage </tag> <tt>Integer_Type string (obj)</tt>
<tag> Description </tag>
   The <tt>string</tt> function may be used to convert an object
   <tt>obj</tt> of any type to a string representation.
   For example, <tt>string(12.34)</tt> returns <tt>"12.34"</tt>.
<tag> Example </tag>
<tscreen><verb>
     define print_anything (anything)
     {
        message (string (anything));
     }
</verb></tscreen>
<tag> Notes </tag>
   This function is <em>not</em> the same as typecasting to a <tt>String_Type</tt>
   using the <tt>typecast</tt> function.
<tag> See Also </tag> <tt>typecast, sprintf, integer, char</tt>
</descrip><p>

<sect><bf>tolower</bf><label id="tolower"><p><descrip>
<tag> Synopsis </tag> Convert a character to lowercase.
<tag> Usage </tag> <tt>Integer_Type lower (Integer_Type ch)</tt>
<tag> Description </tag>
  This function takes an integer <tt>ch</tt> and returns its lowercase
  equivalent.
<tag> See Also </tag> <tt>toupper, strup, strlow, int, char, define_case</tt>
</descrip><p>

<sect><bf>toupper</bf><label id="toupper"><p><descrip>
<tag> Synopsis </tag> Convert a character to uppercase.
<tag> Usage </tag> <tt>Integer_Type toupper (Integer_Type ch)</tt>
<tag> Description </tag>
  This function takes an integer <tt>ch</tt> and returns its uppercase
  equivalent.
<tag> See Also </tag> <tt>tolower, strup, strlow, int, char, define_case</tt>
</descrip><p>

<sect><bf>typecast</bf><label id="typecast"><p><descrip>
<tag> Synopsis </tag> Convert an object from one data type to another.
<tag> Usage </tag> <tt>typecast (x, new_type)</tt>
<tag> Description </tag>
  The <tt>typecast</tt> function performs a generic typecast operation on
  <tt>x</tt> to convert it to <tt>new_type</tt>.  If <tt>x</tt> represents an
  array, the function will attempt to convert all elements of <tt>x</tt>
  to <tt>new_type</tt>.  Not all objects can be converted and a
  type-mismatch error will result upon failure.
<tag> Example </tag>
<tscreen><verb>
    define to_complex (x)
    {
       return typecast (x, Complex_Type);
    }
</verb></tscreen>
  defines a function that converts its argument, <tt>x</tt> to a complex
  number.
<tag> See Also </tag> <tt>int, double, typeof</tt>
</descrip><p>

<sect><bf>typeof</bf><label id="typeof"><p><descrip>
<tag> Synopsis </tag> Get the data type of an object.
<tag> Usage </tag> <tt>DataType_Type typeof (x)</tt>
<tag> Description </tag>
  This function returns the data type of <tt>x</tt>.
<tag> Example </tag>
<tscreen><verb>
  if (Integer_Type == typeof (x)) message ("x is an integer");
</verb></tscreen>
<tag> See Also </tag> <tt>_typeof, is_struct_type, array_info, _slang_guess_type, typecast</tt>
</descrip><p>


<chapt>Stdio File I/O Functions<p>
<sect><bf>clearerr</bf><label id="clearerr"><p><descrip>
<tag> Synopsis </tag> Clear the error of a file stream
<tag> Usage </tag> <tt>clearerr (File_Type fp</tt>
<tag> Description </tag>
  The <tt>clearerr</tt> function clears the error and end-of-file flags
  associated with the open file stream <tt>fp</tt>.
<tag> See Also </tag> <tt>ferror, feof, fopen</tt>
</descrip><p>

<sect><bf>fclose</bf><label id="fclose"><p><descrip>
<tag> Synopsis </tag> Close a file
<tag> Usage </tag> <tt>Integer_Type fclose (File_Type fp)</tt>
<tag> Description </tag>
  The <tt>fclose</tt> function may be used to close an open file pointer
  <tt>fp</tt>.  Upon success it returns zero, and upon failure it sets
  <tt>errno</tt> and returns <tt>-1</tt>.  Failure usually indicates a that
  the file system is full or that <tt>fp</tt> does not refer to an open file.
<tag> Notes </tag>
  Many C programmers call <tt>fclose</tt> without checking the return
  value.  The <bf>S-lang</bf> language requires the programmer to explicitly
  handle any value returned by a <bf>S-lang</bf> function.  The simplest way to
  handle the return value from <tt>fclose</tt> is to use it as:
<tscreen><verb>
     () = fclose (fp);
</verb></tscreen>
<tag> See Also </tag> <tt>fopen, fgets, fflush, pclose, errno</tt>
</descrip><p>

<sect><bf>fdopen</bf><label id="fdopen"><p><descrip>
<tag> Synopsis </tag> Convert a FD_Type file descriptor to a stdio File_Type object
<tag> Usage </tag> <tt>File_Type fdopen (FD_Type, String_Type mode)</tt>
<tag> Description </tag>
   The <tt>fdopen</tt> function creates and returns a stdio
   <tt>File_Type</tt> object from the open <tt>FD_Type</tt>
   descriptor <tt>fd</tt>.  The <tt>mode</tt> parameter corresponds to the
   <tt>mode</tt> parameter of the <tt>fopen</tt> function and must be
   consistent with the mode of the descriptor <tt>fd</tt>.  The function
   returns <tt>NULL</tt> upon failure and sets <tt>errno</tt>.
<tag> Notes </tag>
   The <tt>fclose</tt> function does not close the <tt>File_Type</tt> object
   returned from this function.  The underlying file object must be
   closed by the <tt>close</tt> function.
<tag> See Also </tag> <tt>fileno, fopen, open, close, fclose</tt>
</descrip><p>

<sect><bf>feof</bf><label id="feof"><p><descrip>
<tag> Synopsis </tag> Get the end-of-file status
<tag> Usage </tag> <tt>Integer_Type feof (File_Type fp)</tt>
<tag> Description </tag>
  This function may be used to determine the state of the end-of-file
  indicator of the open file descriptor <tt>fp</tt>.  It returns <tt>0</tt>
  if the indicator is not set, or non-zero if it is.  The end-of-file
  indicator may be cleared by the <tt>clearerr</tt> function.
<tag> See Also </tag> <tt>ferror, clearerr, fopen</tt>
</descrip><p>

<sect><bf>ferror</bf><label id="ferror"><p><descrip>
<tag> Synopsis </tag> Determine the error status of an open file descriptor
<tag> Usage </tag> <tt>Integer_Type ferror (File_Type fp)</tt>
<tag> Description </tag>
  This function may be used to determine the state of the error
  indicator of the open file descriptor <tt>fp</tt>.  It returns <tt>0</tt>
  if the indicator is not set, or non-zero if it is.  The error
  indicator may be cleared by the <tt>clearerr</tt> function.
<tag> See Also </tag> <tt>feof, clearerr, fopen</tt>
</descrip><p>

<sect><bf>fflush</bf><label id="fflush"><p><descrip>
<tag> Synopsis </tag> Flush an output stream
<tag> Usage </tag> <tt>Integer_Type fflush (File_Type fp)</tt>
<tag> Description </tag>
  The <tt>fflush</tt> function may be used to update the <em>output</em>
  stream specified by <tt>fp</tt>.  It returns <tt>0</tt> upon success, or
  <tt>-1</tt> upon failure and sets <tt>errno</tt> accordingly.  In
  particular, this function will fail if <tt>fp</tt> does not represent
  an output stream, or if <tt>fp</tt> is associated with a disk file and
  there is insufficient disk space.
<tag> Example </tag>
  This example illustrates how to use the <tt>fflush</tt> function
  without regard to the return value:
<tscreen><verb>
    () = fputs ("Enter value&gt; ", stdout);
    () = fflush (stdout);
</verb></tscreen>
<tag> Notes </tag>
  Many C programmers disregard the return value from the <tt>fflush</tt>
  function.  The above example illustrates how to properly do this in
  the <bf>S-lang</bf> langauge.
<tag> See Also </tag> <tt>fopen, fclose</tt>
</descrip><p>

<sect><bf>fgets</bf><label id="fgets"><p><descrip>
<tag> Synopsis </tag> Read a line from a file.
<tag> Usage </tag> <tt>Integer_Type fgets (SLang_Ref_Type ref, File_Type fp)</tt>
<tag> Description </tag>
  <tt>fgets</tt> reads a line from the open file specified by <tt>fp</tt>
  and places the characters in the variable whose reference is
  specified by <tt>ref</tt>.
  It returns <tt>-1</tt> if <tt>fp</tt> is not associated with an open file
  or an attempt was made to read at the end the file; otherwise, it
  returns the number of characters read.
<tag> Example </tag>
  The following example returns the lines of a file via a linked list:
<tscreen><verb>
    define read_file (file)
    {
       variable buf, fp, root, tail;
       variable list_type = struct { text, next };

       root = NULL;

       fp = fopen(file, "r");
       if (fp == NULL)
         error("fopen %s failed." file);
       while (-1 != fgets (&amp;buf, fp))
         {
            if (root == NULL)
              {
                 root = @list_type;
                 tail = root;
              }
            else
              {
                 tail.next = @list_type;
                 tail = tail.next;
              }
            tail.text = buf;
            tail.next = NULL;
         }
       () = fclose (fp);
       return root;
    }
</verb></tscreen>
<tag> See Also </tag> <tt>fopen, fclose, fputs, fread, error</tt>
</descrip><p>

<sect><bf>fgetslines</bf><label id="fgetslines"><p><descrip>
<tag> Synopsis </tag> Read all the lines from an open file
<tag> Usage </tag> <tt>String_Type[] fgetslines (File_Type fp)</tt>
<tag> Description </tag>
  The <tt>fgetslines</tt> function returns all the remaining lines as an
  array of strings in the file specified by the open file pointer
  <tt>fp</tt>.  If the file is empty, an empty string array will be
  returned.  The function returns <tt>NULL</tt> upon error.
<tag> Example </tag>
  The following function returns the number of lines in a file:
<tscreen><verb>
    define count_lines_in_file (file)
    {
       variable fp, lines;

       fp = fopen (file, "r");
       if (fp == NULL)
         return -1;
       
       lines = fgetslines (fp);
       if (lines == NULL)
         return -1;
       
       return length (lines);
    }
</verb></tscreen>
  Note that the file was implicitly closed by the function.
<tag> Notes </tag>
  This function should not be used if the file contains many lines
  since that would require that all the lines be read into memory.
<tag> See Also </tag> <tt>fgets, fread, fopen</tt>
</descrip><p>

<sect><bf>fopen</bf><label id="fopen"><p><descrip>
<tag> Synopsis </tag> Open a file
<tag> Usage </tag> <tt>File_Type fopen (String_Type f, String_Type m)</tt>
<tag> Description </tag>
  The <tt>fopen</tt> function opens a file <tt>f</tt> according to the mode
  string <tt>m</tt>.  Allowed values for <tt>m</tt> are:
<tscreen><verb>
     "r"    Read only
     "w"    Write only
     "a"    Append
     "r+"   Reading and writing at the beginning of the file.
     "w+"   Reading and writing.  The file is created if it does not
              exist; otherwise, it is truncated.
     "a+"   Reading and writing at the end of the file.  The file is created
              if it does not already exist.
</verb></tscreen>
  In addition, the mode string can also include the letter <tt>'b'</tt>
  as the last character to indicate that the file is to be opened in
  binary mode.

  Upon success, <tt>fopen</tt> a <tt>File_Type</tt> object which is meant to
  be used in other operations that require an open file.  Upon
  failure, the function returns <tt>NULL</tt>.
<tag> Example </tag>
  The following function opens a file in append mode and writes a
  string to it:
<tscreen><verb>
    define append_string_to_file (file, str)
    {
       variable fp = fopen (file, "a");
       if (fp == NULL) verror ("%s could not be opened", file);
       () = fputs (string, fp);
       () = fclose (fp);
    }
</verb></tscreen>
  Note that the return values from <tt>fputs</tt> and <tt>fclose</tt> are
  ignored.
<tag> Notes </tag>
  There is no need to explicitly close a file opened with <tt>fopen</tt>.
  If the returned <tt>File_Type</tt> object goes out of scope, <bf>S-lang</bf>
  will automatically close the file.  However, explicitly closing a
  file after use is recommended.
<tag> See Also </tag> <tt>fclose, fgets, fputs, popen</tt>
</descrip><p>

<sect><bf>fprintf</bf><label id="fprintf"><p><descrip>
<tag> Synopsis </tag> Create and write a formatted string to a file
<tag> Usage </tag> <tt>Int_Type fprintf (File_Type fp, String_Type fmt, ...)</tt>
<tag> Description </tag>
  <tt>fprintf</tt> formats the objects specified by the variable argument
  list according to the format <tt>fmt</tt> and write the result to the
  open file pointer <tt>fp</tt>.  
  
  The format string obeys the same syntax and semantics as the
  <tt>sprintf</tt> format string.  See the description of the
  <tt>sprintf</tt> function for more information.
  
  <tt>fprintf</tt> returns the number of characters written to the file,
  or <tt>-1</tt> upon error.
<tag> See Also </tag> <tt>fputs, printf, fwrite, message</tt>
</descrip><p>

<sect><bf>fputs</bf><label id="fputs"><p><descrip>
<tag> Synopsis </tag> Write a string to an open stream
<tag> Usage </tag> <tt>Integer_Type fputs (String_Type s, File_Type fp);</tt>
<tag> Description </tag>
  The <tt>fputs</tt> function writes the string <tt>s</tt> to the open file
  pointer <tt>fp</tt>. It returns -1 upon failure and sets <tt>errno</tt>,
  otherwise it returns the length of the string.
<tag> Example </tag>
  The following function opens a file in append mode and uses the
  <tt>fputs</tt> function to write to it.
<tscreen><verb>
    define append_string_to_file (str, file)
    {
       variable fp;
       fp = fopen (file, "a");
       if (fp == NULL) verror ("Unable to open %s", file);
       if ((-1 == fputs (s, fp))
           or (-1 == fclose (fp)))
         verror ("Error writing to %s", file);
    }
</verb></tscreen>
<tag> Notes </tag>
  One must not disregard the return value from the <tt>fputs</tt>
  function, as many C programmers do.  Doing so may lead to a stack
  overflow error.
  
  To write an object that contains embedded null characters, use the
  <tt>fwrite</tt> function.
<tag> See Also </tag> <tt>fclose, fopen, fgets, fwrite</tt>
</descrip><p>

<sect><bf>fread</bf><label id="fread"><p><descrip>
<tag> Synopsis </tag> Read binary data from a file
<tag> Usage </tag> <tt>UInt_Type fread (Ref_Type b, DataType_Type t, UInt_Type n, File_Type fp)</tt>
<tag> Description </tag>
  The <tt>fread</tt> function may be used to read <tt>n</tt> objects of type
  <tt>t</tt> from an open file pointer <tt>fp</tt>.  Upon success, it
  returns the number of objects read from the file and places the
  objects in the variable specified by <tt>b</tt>.  Upon error or end of
  file, it returns <tt>-1</tt>.  If more than one object is read from the
  file, those objects will be placed in an array of the appropriate
  size.  The exception to this is when reading <tt>Char_Type</tt> or
  <tt>UChar_Type</tt> objects from a file, in which case the data will be
  returned as an <tt>n</tt> character BString_Type binary string, but
  only if <tt>n</tt>&gt;1.
<tag> Example </tag>
  The following example illustrates how to read 50 bytes from a file:
<tscreen><verb>
     define read_50_bytes_from_file (file)
     {
        variable fp, n, buf;
        
        fp = fopen (file, "rb");
        if (fp == NULL) error ("Open failed");
        n = fread (&amp;buf, Char_Type, 50, fp);
        if (n == -1)
        error ("fread failed");
        () = fclose (fp);
        return buf;
     }
</verb></tscreen>
<tag> Notes </tag>
  Use the <tt>pack</tt> and <tt>unpack</tt> functions to read data with a
  specific byte-ordering.
<tag> See Also </tag> <tt>fwrite, fgets, fopen, pack, unpack</tt>
</descrip><p>

<sect><bf>fseek</bf><label id="fseek"><p><descrip>
<tag> Synopsis </tag> Reposition a stream
<tag> Usage </tag> <tt>Integer_Type fseek (File_Type fp, Integer_Type ofs, Integer_Type whence</tt>
<tag> Description </tag>
  The <tt>fseek</tt> function may be used to reposition the file position
  pointer associated with the open file stream <tt>fp</tt>. Specifically,
  it moves the pointer <tt>ofs</tt> bytes relative to the position
  indicated by <tt>whence</tt>.  If whence is set to one of the symbolic
  constants <tt>SEEK_SET</tt>, <tt>SEEK_CUR</tt>, or <tt>SEEK_END</tt>, the
  offset is relative to the start of the file, the current position
  indicator, or end-of-file, respectively.
  
  The function return zero upon success, or <tt>-1</tt> upon failure and sets
  <tt>errno</tt> accordingly.
<tag> Example </tag>
    define rewind (fp)
    {
       if (0 == fseek (fp, 0, SEEK_SET)) return;
       vmessage ("rewind failed, reason: %s", errno_string (errno));
    }
<tag> Notes </tag>
  The current implementation uses an integer to specify the offset.
  One some systems, a long integer may be required making this
  function fail for very large files, i.e., files that are longer than
  the maximum value of an integer.
<tag> See Also </tag> <tt>ftell, fopen</tt>
</descrip><p>

<sect><bf>ftell</bf><label id="ftell"><p><descrip>
<tag> Synopsis </tag> Obtain the current position in an open stream
<tag> Usage </tag> <tt>Integer_Type ftell (File_Type fp)</tt>
<tag> Description </tag>
  The ftell function may be used to obtain the current position in the
  stream associated with the open file pointer <tt>fp</tt>.  It returns
  the position of the pointer measured in bytes from the beginning of
  the file.  Upon error, it returns <tt>-1</tt> and sets <tt>errno</tt>.
<tag> See Also </tag> <tt>fseek, fopen</tt>
</descrip><p>

<sect><bf>fwrite</bf><label id="fwrite"><p><descrip>
<tag> Synopsis </tag> Write binary data to a file
<tag> Usage </tag> <tt>UInt_Type fwrite (b, File_Type fp)</tt>
<tag> Description </tag>
  The <tt>fwrite</tt> may be used to write the object represented by
  <tt>b</tt> to an open file.  If <tt>b</tt> is a string or an array, the
  function will attempt to write all elements of the object to the
  file.  It returns the number of objects successfully written,
  otherwise it returns <tt>-1</tt> upon error and sets <tt>errno</tt>
  accordingly.
<tag> Example </tag>
  The following example illustrates how to write an integer array to a
  file.  In this example, <tt>fp</tt> is an open file descriptor:
<tscreen><verb>
     variable a = [1:50];     % 50 element integer array
     if (50 != fwrite (a, fp))
       error ("fwrite failed");
</verb></tscreen>
  Here is how to write the array one element at a time:
<tscreen><verb>
     variable a = [1:50];
     foreach (a)
       {
          variable ai = ();
          if (1 != fwrite(ai, fp))
          error ("fwrite failed");
       }
</verb></tscreen>
<tag> Notes </tag>
  Not all data types may support the <tt>fwrite</tt> operation.  However,
  it is supported by all vector, scalar, and string objects.
<tag> See Also </tag> <tt>fread, fputs, fopen, pack, unpack</tt>
</descrip><p>

<sect><bf>pclose</bf><label id="pclose"><p><descrip>
<tag> Synopsis </tag> Close an object opened with popen
<tag> Usage </tag> <tt>Integer_Type pclose (File_Type fp)</tt>
<tag> Description </tag>
  The <tt>pclose</tt> function waits for the process associated with
  <tt>fp</tt> to exit and the returns the exit status of the command.
<tag> See Also </tag> <tt>pclose, fclose</tt>
</descrip><p>

<sect><bf>popen</bf><label id="popen"><p><descrip>
<tag> Synopsis </tag> Open a process
<tag> Usage </tag> <tt>File_Type popen (String_Type cmd, String_Type mode)</tt>
<tag> Description </tag>
  The <tt>popen</tt> function executes a process specified by <tt>cmd</tt>
  and opens a unidirectional pipe to the newly created process.  The
  <tt>mode</tt> indicates whether or not the the pipe is open for reading
  or writing.  Specifically, if <tt>mode</tt> is <tt>"r"</tt>, then the
  pipe is opened for reading, or if <tt>mode</tt> is <tt>"w"</tt>, then the
  pipe will be open for writing.

  Upon success, a <tt>File_Type</tt> pointer will be returned, otherwise
  the function failed and <tt>NULL</tt> will be returned.
<tag> Notes </tag>
  This function is not available on all systems.
<tag> See Also </tag> <tt>pclose, fopen</tt>
</descrip><p>

<sect><bf>printf</bf><label id="printf"><p><descrip>
<tag> Synopsis </tag> Create and write a formatted string to stdout
<tag> Usage </tag> <tt>Int_Type printf (String_Type fmt, ...)</tt>
<tag> Description </tag>
  <tt>fprintf</tt> formats the objects specified by the variable argument
  list according to the format <tt>fmt</tt> and write the result to
  <tt>stdout</tt>.  This function is equivalent to <tt>fprintf</tt> used
  with the <tt>stdout</tt> file pointer.  See <tt>fprintf</tt> for more
  information.
  
  <tt>printf</tt> returns the number of characters written to the file,
  or <tt>-1</tt> upon error.
<tag> Notes </tag>
  Many C programmers do not check the return status of the
  <tt>printf</tt> C library function.  Make sure that if you do not care
  about whether or not the function succeeds, then code it as in the
  following example:
<tscreen><verb>
     () = printf ("%s laid %d eggs\n", chicken_name, num_egg);
</verb></tscreen>
<tag> See Also </tag> <tt>fputs, printf, fwrite, message</tt>
</descrip><p>


<chapt>Low-level POSIX I/O functions<p>
<sect><bf>close</bf><label id="close"><p><descrip>
<tag> Synopsis </tag> Close an open file descriptor
<tag> Usage </tag> <tt>Int_Type close (FD_Type fd)</tt>
<tag> Description </tag>
  The <tt>close</tt> function is used to open file descriptor of type
  <tt>FD_Type</tt>.  Upon success <tt>0</tt> is returned, otherwise the function
  returns <tt>-1</tt> and sets <tt>errno</tt> accordingly.
<tag> See Also </tag> <tt>open, fclose, read, write</tt>
</descrip><p>

<sect><bf>dup_fd</bf><label id="dup_fd"><p><descrip>
<tag> Synopsis </tag> Duplicate a file descriptor
<tag> Usage </tag> <tt>FD_Type dup_fd (FD_Type fd)</tt>
<tag> Description </tag>
  The <tt>dup_fd</tt> function duplicates and file descriptor and returns
  its duplicate.  If the function fails, <tt>NULL</tt> will be returned and
  <tt>errno</tt> set accordingly.
<tag> Notes </tag>
  This function is essentually a wrapper around the POSIX <tt>dup</tt>
  function.
<tag> See Also </tag> <tt>open, close</tt>
</descrip><p>

<sect><bf>fileno</bf><label id="fileno"><p><descrip>
<tag> Synopsis </tag> Convert a stdio File_Type object to a FD_Type descriptor
<tag> Usage </tag> <tt>FD_Type fileno (File_Type fp)</tt>
<tag> Description </tag>
  The <tt>fileno</tt> function returns the <tt>FD_Type</tt> descriptor
  associated with the <tt>File_Type</tt> file pointer.  Upon failure,
  <tt>NULL</tt> is returned.
<tag> See Also </tag> <tt>fopen, open, fclose, close, dup_fd</tt>
</descrip><p>

<sect><bf>isatty</bf><label id="isatty"><p><descrip>
<tag> Synopsis </tag> Determine if an open file descriptor refers to a terminal
<tag> Usage </tag> <tt>Int_Type isatty (FD_Type or File_Type fd)</tt>
<tag> Description </tag>
  This function returns <tt>1</tt> if the file descriptor <tt>fd</tt> refers to a
  terminal; otherwise it returns <tt>0</tt>.  The object <tt>fd</tt> may either
  be a <tt>File_Type</tt> stdio descriptor or an <tt>FD_Type</tt> object.
<tag> See Also </tag> <tt>fopen, fclose, fileno</tt>
</descrip><p>

<sect><bf>lseek</bf><label id="lseek"><p><descrip>
<tag> Synopsis </tag> Reposition a file descriptor's file pointer
<tag> Usage </tag> <tt>Long_Type lseek (FD_Type fd, Long_Type ofs, int mode)</tt>
   The <tt>lseek</tt> function repositions the file pointer associated
   with the open file descriptor <tt>fp</tt> to offset <tt>ofs</tt>
   according to the mode parameter.  Specifically, <tt>mode</tt> must be
   one of the values:
<tscreen><verb>
     SEEK_SET   Set the offset to ofs
     SEEK_CUR   Add ofs to the current offset
     SEEK_END   Add ofs to the current file size
</verb></tscreen>
   Upon error, <tt>lseek</tt> returns <tt>-1</tt> and sets <tt>errno</tt>.  If
   successful, it returns the new filepointer offset.
<tag> Notes </tag>
   Not all file descriptors are capable of supporting the seek
   operation, e.g., a descriptor associated with a pipe.
   
   By using <tt>SEEK_END</tt> with a positive value of the <tt>ofs</tt>
   parameter, it is possible to position the file pointer beyond the
   current size of the file.
<tag> See Also </tag> <tt>fseek, ftell, open, close</tt>
</descrip><p>

<sect><bf>open</bf><label id="open"><p><descrip>
<tag> Synopsis </tag> Open a file
<tag> Usage </tag> <tt>FD_Type open (String_Type filename, Int_Type flags [,Int_Type mode])</tt>
<tag> Description </tag>
  The <tt>open</tt> function attempts to open a file specified by the
  <tt>filename</tt> parameter according to the <tt>flags</tt> parameter,
  which must be one of the following values:
<tscreen><verb>
     O_RDONLY   (read-only)
     O_WRONLY   (write-only)
     O_RDWR     (read/write)
</verb></tscreen>
  In addition, <tt>flags</tt> may also be bitwise-or'd with any of the
  following:
<tscreen><verb>
     O_BINARY   (open the file in binary mode)
     O_TEXT     (open the file in text mode)
     O_CREAT    (create file if it does not exist)
     O_EXCL     (fail if the file already exists)
     O_NOCTTY   (do not make the device the controlling terminal)
     O_TRUNC    (truncate the file if it exists)
     O_APPEND   (open the file in append mode)
     O_NONBLOCK (open the file in non-blocking mode)
</verb></tscreen>
   Some of these flags only make sense when combined with other flags.
   For example, if O_EXCL is used, then O_CREAT must also be
   specified, otherwise unpredictable behavior may result.

   If <tt>O_CREAT</tt> is used for the <tt>flags</tt> parameter then the
   <tt>mode</tt> parameter must be present. <tt>mode</tt> specifies the
   permissions to use if a new file is created. The actual file
   permissions will be affected by the process's <tt>umask</tt> via
   <tt>mode&amp;~umask</tt>.  The <tt>mode</tt> parameter's value is
   constructed via bitwise-or of the following values:
<tscreen><verb>
     S_IRWXU    (Owner has read/write/execute permission)
     S_IRUSR    (Owner has read permission)
     S_IWUSR    (Owner has write permission)
     S_IXUSR    (Owner has execute permission)
     S_IRWXG    (Group has read/write/execute permission)
     S_IRGRP    (Group has read permission)
     S_IWGRP    (Group has write permission)
     S_IXGRP    (Group has execute permission)
     S_IRWXO    (Others have read/write/execute permission)
     S_IROTH    (Others have read permission)
     S_IWOTH    (Others have write permission)
     S_IXOTH    (Others have execute permission)
</verb></tscreen>
   Upon success <tt>open</tt> returns a file descriptor object
   (<tt>FD_Type</tt>), otherwise <tt>NULL</tt> is returned and <tt>errno</tt>
   is set.
<tag> Notes </tag>
   If you are not familiar with the <tt>open</tt> system call, then it
   is recommended that you use <tt>fopen</tt> instead.
<tag> See Also </tag> <tt>fopen, close, read, write, stat_file</tt>
</descrip><p>

<sect><bf>read</bf><label id="read"><p><descrip>
<tag> Synopsis </tag> Read from an open file descriptor
<tag> Usage </tag> <tt>UInt_Type read (FD_Type fd, Ref_Type buf, UInt_Type num)</tt>
<tag> Description </tag>
  The <tt>read</tt> function attempts to read at most <tt>num</tt> bytes
  into the variable indicated by <tt>buf</tt> from the open file
  descriptor <tt>fd</tt>.  It returns the number of bytes read, or <tt>-1</tt>
  and sets <tt>errno</tt> upon failure.  The number of bytes read may be
  less than <tt>num</tt>, and will be zero if an attempt is made to read
  past the end of the file.
<tag> Notes </tag>
  <tt>read</tt> is a low-level function and may return <tt>-1</tt> for a variety
  of reasons.  For example, if non-blocking I/O has been specified for
  the open file descriptor and no data is available for reading then
  the function will return <tt>-1</tt> and set <tt>errno</tt> to <tt>EAGAIN</tt>.
<tag> See Also </tag> <tt>fread, open, close, write</tt>
</descrip><p>  

<sect><bf>write</bf><label id="write"><p><descrip>
<tag> Synopsis </tag> Write to an open file descriptor
<tag> Usage </tag> <tt>UInt_Type write (FD_Type fd, BString_Type buf)</tt>
<tag> Description </tag>
   The <tt>write</tt> function attempts to write the bytes specified by
   the <tt>buf</tt> parameter to the open file descriptor <tt>fd</tt>.  It
   returns the number of bytes successfully written, or <tt>-1</tt> and sets
   <tt>errno</tt> upon failure.  The number of bytes written may be less
   than <tt>length(buf)</tt>.
<tag> See Also </tag> <tt>read, fwrite, open, close</tt>
</descrip><p>


<chapt>Directory Functions<p>
<sect><bf>chdir</bf><label id="chdir"><p><descrip>
<tag> Synopsis </tag> Change the current working directory.
<tag> Usage </tag> <tt>Integer_Type chdir (String_Type dir)</tt>
<tag> Description </tag>
  The <tt>chdir</tt> function may be used to changed the current working
  directory to the directory specified by <tt>dir</tt>.  Upon sucess it
  returns zero; however, upon failure it returns <tt>-1</tt> and sets
  <tt>errno</tt> accordingly.
<tag> See Also </tag> <tt>mkdir, stat_file</tt>
</descrip><p>

<sect><bf>chmod</bf><label id="chmod"><p><descrip>
<tag> Synopsis </tag> Change the mode of a file
<tag> Usage </tag> <tt>Integer_Type chmod (String_Type file, Integer_Type mode)</tt>
<tag> Description </tag>
  The <tt>chmod</tt> function changes the permissions of <tt>file</tt> to those
  specified by <tt>mode</tt>.  It returns <tt>0</tt> upon success, or
  <tt>-1</tt> upon failure setting <tt>errno</tt> accordingly.

  See the system specific documentation for the C library
  function <tt>chmod</tt> for a discussion of the <tt>mode</tt> parameter.
<tag> See Also </tag> <tt>chown, stat_file</tt>
</descrip><p>

<sect><bf>chown</bf><label id="chown"><p><descrip>
<tag> Synopsis </tag> Change the owner of a file
<tag> Usage </tag> <tt>Integer_Type chown (String_Type file, Integer_Type uid, Integer_Type gid)</tt>
<tag> Description </tag>
  The <tt>chown</tt> function is used to change the user-id and group-id of
  <tt>file</tt> to <tt>uid</tt> and <tt>gid</tt>, respectively.  It returns
  <tt>zero</tt> upon success and <tt>-1</tt> upon failure, with <tt>errno</tt>
  set accordingly.
<tag> Notes </tag>
  On most systems, only the super user can change the ownership of a
  file.

  Some systems do not support this function.
<tag> See Also </tag> <tt>chmod, stat_file</tt>
</descrip><p>

<sect><bf>getcwd</bf><label id="getcwd"><p><descrip>
<tag> Synopsis </tag> Get the current working directory
<tag> Usage </tag> <tt>String_Type getcwd ()</tt>
<tag> Description </tag>
  The <tt>getcwd</tt> function returns the absolute pathname of the
  current working directory.  If an error occurs or it cannot
  determine the working directory, it returns <tt>NULL</tt> and sets
  <tt>errno</tt> accordingly.
<tag> Notes </tag>
  Under Unix, OS/2, and MSDOS, the pathname returned by this function
  includes the trailing slash character.  Some versions also include
  the drive specifier.
<tag> See Also </tag> <tt>mkdir, chdir, errno</tt>
</descrip><p>

<sect><bf>listdir</bf><label id="listdir"><p><descrip>
<tag> Synopsis </tag> Get a list of the files in a directory
<tag> Usage </tag> <tt>String_Type[] listdir (String_Type dir)</tt>
<tag> Description </tag>
  The <tt>listdir</tt> function returns the directory listing of all the
  files in the specified directory <tt>dir</tt> as an array of strings.
  It does not return the special files <tt>".."</tt> and <tt>"."</tt> as
  part of the list.
<tag> See Also </tag> <tt>stat_file, stat_is, length</tt>
</descrip><p>

<sect><bf>lstat_file</bf><label id="lstat_file"><p><descrip>
<tag> Synopsis </tag> Get information about a symbolic link
<tag> Usage </tag> <tt>Struct_Type lstat_file (String_Type file)</tt>
<tag> Description </tag>
  The <tt>lstat_file</tt> function behaves identically to <tt>stat_file</tt>
  but if <tt>file</tt> is a symbolic link, <tt>lstat_file</tt> returns
  information about the link itself, and not the file that it
  references.

  See the documentation for <tt>stat_file</tt> for more information.
<tag> Notes </tag>
  On systems that do not support symbolic links, there is no
  difference between this function and the <tt>stat_file</tt> function.
<tag> See Also </tag> <tt>stat_file, readlink</tt>
</descrip><p>

<sect><bf>mkdir</bf><label id="mkdir"><p><descrip>
<tag> Synopsis </tag> Create a new directory
<tag> Usage </tag> <tt>Integer_Type mkdir (String_Type dir, Integer_Type mode)</tt>
<tag> Description </tag>
  The <tt>mkdir</tt> function creates a directory whose name is specified
  by the <tt>dir</tt> parameter with permissions specified by <tt>mode</tt>.
  Upon success <tt>mkdir</tt> returns zero, or it returns <tt>-1</tt> and
  sets <tt>errno</tt> accordingly.  In particular, if the directory
  already exists, the function will fail and set errno to
  <tt>EEXIST</tt>.
<tag> Example </tag>
<tscreen><verb>
     define my_mkdir (dir)
     {
        if (0 == mkdir (dir, 0777)) return;
        if (errno == EEXIST) return;
        verror ("mkdir %s failed: %s", dir, errno_string (errno));
     }
</verb></tscreen>
<tag> Notes </tag>
  The <tt>mode</tt> parameter may not be meaningful on all systems.  On
  systems where it is meaningful, the actual permissions on the newly
  created directory are modified by the process's umask.
<tag> See Also </tag> <tt>rmdir, getcwd, chdir, fopen, errno</tt>
</descrip><p>

<sect><bf>readlink</bf><label id="readlink"><p><descrip>
<tag> Synopsis </tag> String_Type readlink (String_Type path)
<tag> Usage </tag> <tt>Get the value of a symbolic link</tt>
<tag> Description </tag>
  The <tt>readlink</tt> function returns the value of a symbolic link and
  returns it as a string.  Upon failure, <tt>NULL</tt> is returned and
  <tt>errno</tt> set accordingly.
<tag> Notes </tag>
  Not all systems support this function.
<tag> See Also </tag> <tt>lstat_file, stat_file, stat_is</tt>
</descrip><p>

<sect><bf>remove</bf><label id="remove"><p><descrip>
<tag> Synopsis </tag> Delete a file
<tag> Usage </tag> <tt>Integer_Type remove (String_Type file)</tt>
<tag> Description </tag>
  The <tt>remove</tt> function deletes a file.  It returns <tt>0</tt> upon
  success, or <tt>-1</tt> upon error and sets <tt>errno</tt> accordingly.
<tag> See Also </tag> <tt>rename, rmdir</tt>
</descrip><p>

<sect><bf>rename</bf><label id="rename"><p><descrip>
<tag> Synopsis </tag> Rename a file
<tag> Usage </tag> <tt>Integer_Type rename (String_Type old, String_Type new)</tt>
<tag> Description </tag>
  The <tt>rename</tt> function renames a file from <tt>old</tt> to <tt>new</tt>
  moving it between directories if necessary.  This function may fail
  if the directories do not refer to the same file system.  It returns
  <tt>0</tt> upon success, or <tt>-1</tt> upon error and sets <tt>errno</tt> accordingly.
<tag> See Also </tag> <tt>remove, errno</tt>
</descrip><p>

<sect><bf>rmdir</bf><label id="rmdir"><p><descrip>
<tag> Synopsis </tag> Remove a directory
<tag> Usage </tag> <tt>Integer_Type rmdir (String_Type dir)</tt>
<tag> Description </tag>
  The <tt>rmdir</tt> function deletes a specified directory.  It returns
  <tt>0</tt> upon success or <tt>-1</tt> upon error and sets <tt>errno</tt> accordingly.
<tag> Notes </tag>
  The directory must be empty before it can be removed.
<tag> See Also </tag> <tt>rename, remove, mkdir</tt>
</descrip><p>

<sect><bf>stat_file</bf><label id="stat_file"><p><descrip>
<tag> Synopsis </tag> Get information about a file
<tag> Usage </tag> <tt>Struct_Type stat_file (String_Type file)</tt>
<tag> Description </tag>
  The <tt>stat_file</tt> function returns information about <tt>file</tt>
  through the use of the system <tt>stat</tt> call.  If the stat call
  fails, the function returns <tt>NULL</tt> and sets errno accordingly.
  If it is successful, it returns a stat structure with the following
  integer fields:
<tscreen><verb>
    st_dev
    st_ino
    st_mode
    st_nlink
    st_uid
    st_gid
    st_rdev
    st_size
    st_atime
    st_mtime
    st_ctime
</verb></tscreen>
  See the man page for <tt>stat</tt> for a discussion of these fields.
<tag> Example </tag>
  The following example shows how the <tt>stat_file</tt> function may be
  used to get the size of a file:
<tscreen><verb>
     define file_size (file)
     {
        variable st;
        st = stat_file(file);
        if (st == NULL) verror ("Unable to stat %s", file);
        return st.st_size;
     }
</verb></tscreen>
<tag> See Also </tag> <tt>lstat_file, stat_is</tt>
</descrip><p>

<sect><bf>stat_is</bf><label id="stat_is"><p><descrip>
<tag> Synopsis </tag> Parse the <tt>st_mode</tt> field of a stat structure
<tag> Usage </tag> <tt>Char_Type stat_is (String_Type type, Integer_Type st_mode)</tt>
<tag> Description </tag>
  The <tt>stat_is</tt> function returns a signed character value about
  the type of file specified by <tt>st_mode</tt>.  Specifically,
  <tt>type</tt> must be one of the strings:
<tscreen><verb>
     "sock"     (socket)
     "fifo"     (fifo)
     "blk"      (block device)
     "chr"      (character device)
     "reg"      (regular file)
     "lnk"      (link)
     "dir"      (dir)
</verb></tscreen>
  It returns a non-zero value if <tt>st_mode</tt> corresponds to
  <tt>type</tt>.
<tag> Example </tag>
  The following example illustrates how to use the <tt>stat_is</tt>
  function to determine whether or not a file is a directory:
<tscreen><verb>
     define is_directory (file)
     {
        variable st;

        st = stat_file (file);
        if (st == NULL) return 0;
        return stat_is ("dir", st.st_mode);
     }
</verb></tscreen>
<tag> See Also </tag> <tt>stat_file, lstat_file</tt>
</descrip><p>


<chapt>Functions that parse pathnames<p>
<sect><bf>path_basename</bf><label id="path_basename"><p><descrip>
<tag> Synopsis </tag> Get the basename part of a pathname
<tag> Usage </tag> <tt>String_Type path_basename (String_Type path)</tt>
<tag> Description </tag>
   The <tt>path_basename</tt> function returns the basename associated
   with the <tt>path</tt> parameter.  The basename is the non-directory
   part of the filename, e.g., on unix <tt>c</tt> is the basename of
   <tt>/a/b/c</tt>.
<tag> See Also </tag> <tt>path_dirname, path_extname, path_concat, path_is_absolute</tt>
</descrip><p>

<sect><bf>path_concat</bf><label id="path_concat"><p><descrip>
<tag> Synopsis </tag> Combine elements of a pathname
<tag> Usage </tag> <tt>String_Type path_concat (String_Type dir, String_Type basename)</tt>
<tag> Description </tag>
   The <tt>path_concat</tt> function combines the arguments <tt>dir</tt> and
   <tt>basename</tt> to produce a pathname.  For example, on unix is
   <tt>dir</tt> is <tt>x/y</tt> and <tt>basename</tt> is <tt>z</tt>, then the
   function will return <tt>x/y/z</tt>.
<tag> See Also </tag> <tt>path_dirname, path_basename, path_extname, path_is_absolute</tt>
</descrip><p>

<sect><bf>path_dirname</bf><label id="path_dirname"><p><descrip>
<tag> Synopsis </tag> Get the directory name part of a pathname
<tag> Usage </tag> <tt>String_Type path_dirname (String_Type path)</tt>
<tag> Description </tag>
   The <tt>path_dirname</tt> function returns the directory name
   associated with a specified pathname.
<tag> Notes </tag>
   On systems that include a drive specifier as part of the pathname,
   the value returned by this function will include the driver
   specifier.
<tag> See Also </tag> <tt>path_basename, path_extname, path_concat, path_is_absolute</tt>
</descrip><p>

<sect><bf>path_extname</bf><label id="path_extname"><p><descrip>
<tag> Synopsis </tag> Return the extension part of a pathname
<tag> Usage </tag> <tt>String_Type path_extname (String_Type path)</tt>
<tag> Description </tag>
   The <tt>path_extname</tt> function returns the extension portion of a
   specified pathname.  If an extension is present, this function will
   also include the dot as part of the extension, i.e., if <tt>path</tt>
   is <tt>file.c</tt>, then this function returns <tt>".c"</tt>.  If no
   extension is present, the function returns an empty string <tt>""</tt>.
<tag> Notes </tag>
   Under VMS, the file version number is not returned as part of the
   extension.
<tag> See Also </tag> <tt>path_sans_extname, path_dirname, path_basename, path_concat, path_is_absolute</tt>
</descrip><p>

<sect><bf>path_is_absolute</bf><label id="path_is_absolute"><p><descrip>
<tag> Synopsis </tag> Determine whether or not a pathname is absolute
<tag> Usage </tag> <tt>Int_Type path_is_absolute (String_Type path)</tt>
<tag> Description </tag>
   The <tt>path_is_absolute</tt> function will return non-zero is
   <tt>path</tt> refers to an absolute pathname, otherwise it returns zero.
<tag> See Also </tag> <tt>path_dirname, path_basename, path_extname, path_concat</tt>
</descrip><p>

<sect><bf>path_sans_extname</bf><label id="path_sans_extname"><p><descrip>
<tag> Synopsis </tag> Strip the extension from a pathname
<tag> Usage </tag> <tt>String_Type path_sans_extname (String_Type path)</tt>
<tag> Description </tag>
  The <tt>path_sans_extname</tt> function removes the file name extension
  (including the dot) from the path and returns the result.
<tag> See Also </tag> <tt>path_extname, path_basename, path_dirname, path_concat</tt>
</descrip><p>


<chapt>System Call Functions<p>
<sect><bf>errno</bf><label id="errno"><p><descrip>
<tag> Synopsis </tag> Error code set by system functions.
<tag> Usage </tag> <tt>Integer_Type errno</tt>
<tag> Description </tag>
  A system function can fail for a variety of reasons.  For example, a
  file operation may fail because lack of disk space, or the process
  does not have permission to perform the operation.  Such functions
  will return <tt>-1</tt> and set the variable <tt>errno</tt> to an error
  code describing the reason for failure.

  Particular values of <tt>errno</tt> may be specified by the following
  symbolic constants (read-only variables) and the corresponding
  <tt>errno_string</tt> value:
<tscreen><verb>
     EPERM            "Not owner"
     ENOENT           "No such file or directory"
     ESRCH            "No such process"
     ENXIO            "No such device or address"
     ENOEXEC          "Exec format error"
     EBADF            "Bad file number"
     ECHILD           "No children"
     ENOMEM           "Not enough core"
     EACCES           "Permission denied"
     EFAULT           "Bad address"
     ENOTBLK          "Block device required"
     EBUSY            "Mount device busy"
     EEXIST           "File exists"
     EXDEV            "Cross-device link"
     ENODEV           "No such device"
     ENOTDIR          "Not a directory"
     EISDIR           "Is a directory"
     EINVAL           "Invalid argument"
     ENFILE           "File table overflow"
     EMFILE           "Too many open files"
     ENOTTY           "Not a typewriter"
     ETXTBSY          "Text file busy"
     EFBIG            "File too large"
     ENOSPC           "No space left on device"
     ESPIPE           "Illegal seek"
     EROFS            "Read-only file system"
     EMLINK           "Too many links"
     EPIPE            "Broken pipe"
     ELOOP            "Too many levels of symbolic links"
     ENAMETOOLONG     "File name too long"
</verb></tscreen>
<tag> Example </tag>
  The <tt>mkdir</tt> function will attempt to create a directory.  If
  that directory already exists, the function will fail and set
  <tt>errno</tt> to <tt>EEXIST</tt>.
<tscreen><verb>
    define create_dir (dir)
    {
       if (0 == mkdir (dir)) return;
       if (errno != EEXIST)
         error ("mkdir %s failied: %s", dir, errno_string);
    }
</verb></tscreen>
<tag> See Also </tag> <tt>errno_string, error, mkdir</tt>
</descrip><p>

<sect><bf>errno_string</bf><label id="errno_string"><p><descrip>
<tag> Synopsis </tag> Return a string describing an errno.
<tag> Usage </tag> <tt>String_Type errno_string (Integer_Type err)</tt>
<tag> Description </tag>
  The <tt>errno_string</tt> function returns a string describing the
  integer error code <tt>err</tt>.  The variable <tt>err</tt> usually
  corresponds to the <tt>errno</tt> intrinsic function.  See the
  description for <tt>errno</tt> for more information.
<tag> Example </tag>
  The <tt>errno_string</tt> function may be used as follows:
<tscreen><verb>
    define sizeof_file (file)
    {
       variable st = stat (file);
       if (st == NULL)
         verror ("%s: %s", file, errno_string (errno);
       return st.st_size;
    }
</verb></tscreen>
<tag> See Also </tag> <tt>errno, stat, verror</tt>
</descrip><p>

<sect><bf>getegid</bf><label id="getegid"><p><descrip>
<tag> Synopsis </tag> Get the effective group id
<tag> Usage </tag> <tt>Int_Type getegid ()</tt>
<tag> Description </tag>
  The <tt>getegid</tt> function returns the effective group ID of the
  current process.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>getgid, geteuid, setgid</tt>
</descrip><p>

<sect><bf>geteuid</bf><label id="geteuid"><p><descrip>
<tag> Synopsis </tag> Get the effective user-id of the current process
<tag> Usage </tag> <tt>Int_Type geteuid ()</tt>
<tag> Description </tag>
  The <tt>geteuid</tt> function returns the effective user-id of the
  current process.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>getuid, setuid, setgid</tt>
</descrip><p>

<sect><bf>getgid</bf><label id="getgid"><p><descrip>
<tag> Synopsis </tag> Get the group id
<tag> Usage </tag> <tt>Integer_Type getgid ()</tt>
<tag> Description </tag>
  The <tt>getgid</tt> function returns the real group id of the current
  process.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>getpid, getppid</tt>
</descrip><p>

<sect><bf>getpid</bf><label id="getpid"><p><descrip>
<tag> Synopsis </tag> Get the current process id
<tag> Usage </tag> <tt>Integer_Type getpid ()</tt>
<tag> Description </tag>
  The <tt>getpid</tt> function returns the current process identification
  number.
<tag> See Also </tag> <tt>getppid, getgid</tt>
</descrip><p>

<sect><bf>getppid</bf><label id="getppid"><p><descrip>
<tag> Synopsis </tag> Get the parent process id
<tag> Usage </tag> <tt>Integer_Type getppid ()</tt>
<tag> Description </tag>
  The <tt>getpid</tt> function returns the process identification
  number of the parent process.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>getpid, getgid</tt>
</descrip><p>

<sect><bf>getuid</bf><label id="getuid"><p><descrip>
<tag> Synopsis </tag> Get the user-id of the current process
<tag> Usage </tag> <tt>Int_Type getuid ()</tt>
<tag> Description </tag>
  The <tt>getuid</tt> function returns the user-id of the current
  process.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>getuid, getegid</tt>
</descrip><p>

<sect><bf>kill</bf><label id="kill"><p><descrip>
<tag> Synopsis </tag> Send a signal to a process
<tag> Usage </tag> <tt>Integer_Type kill (Integer_Type pid, Integer_Type sig)</tt>
<tag> Description </tag>
  This function may be used to send a signal given by the integer <tt>sig</tt>
  to the process specified by <tt>pid</tt>.  The function returns zero upon
  sucess and <tt>-1</tt> upon failure setting errno accordingly.
<tag> Example </tag>
  The <tt>kill</tt> function may be used to determine whether or not
  a specific process exists:
<tscreen><verb>
    define process_exists (pid)
    {
       if (-1 == kill (pid, 0))
         return 0;     % Process does not exist
       return 1;
    }
</verb></tscreen>
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>getpid</tt>
</descrip><p>

<sect><bf>mkfifo</bf><label id="mkfifo"><p><descrip>
<tag> Synopsis </tag> Create a named pipe
<tag> Usage </tag> <tt>Int_Type mkfifo (String_Type name, Int_Type mode)</tt>
<tag> Description </tag>
  The <tt>mkfifo</tt> attempts to create a named pipe with the specified
  name and mode (modified by the process's umask).  The function
  returns <tt>0</tt> upon success, or <tt>-1</tt> and sets <tt>errno</tt> upon failure.
<tag> Notes </tag>
  Not all systems support the <tt>mkfifo</tt> function and even on
  systems that do implement the <tt>mkfifo</tt> system call, the
  underlying file system may not support the concept of a named pipe,
  e.g, an NFS filesystem.
<tag> See Also </tag> <tt>stat_file</tt>
</descrip><p>

<sect><bf>setgid</bf><label id="setgid"><p><descrip>
<tag> Synopsis </tag> Set the group-id of the current process
<tag> Usage </tag> <tt>Int_Type setgid (Int_Type gid)</tt>
<tag> Description </tag>
  The <tt>setgid</tt> function sets the effective group-id of the current
  process.  It returns zero upon success, or <tt>-1</tt> upon error and sets
  <tt>errno</tt> appropriately.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>getgid, setuid</tt>
</descrip><p>

<sect><bf>setpgid</bf><label id="setpgid"><p><descrip>
<tag> Synopsis </tag> Set the process group-id
<tag> Usage </tag> <tt>Int_Type setpgid (Int_Type pid, Int_Type gid)</tt>
<tag> Description </tag>
  The <tt>setpgid</tt> function sets the group-id <tt>gid</tt> of the
  process whose process-id is <tt>pid</tt>.  If <tt>pid</tt> is <tt>0</tt>, then the
  current process-id will be used.  If <tt>pgid</tt> is <tt>0</tt>, then the pid
  of the affected process will be used.
  
  If successful zero will be returned, otherwise the function will
  return <tt>-1</tt> and set <tt>errno</tt> accordingly.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>setgid, setuid</tt>
</descrip><p>

<sect><bf>setuid</bf><label id="setuid"><p><descrip>
<tag> Synopsis </tag> Set the user-id of the current process
<tag> Usage </tag> <tt>Int_Type setuid (Int_Type id)</tt>
<tag> Description </tag>
  The <tt>setuid</tt> function sets the effective user-id of the current
  process.  It returns zero upon success, or <tt>-1</tt> upon error and sets
  <tt>errno</tt> appropriately.
<tag> Notes </tag>
  This function is not supported by all systems.
<tag> See Also </tag> <tt>setgid, setpgid, getuid, geteuid</tt>
</descrip><p>

<sect><bf>sleep</bf><label id="sleep"><p><descrip>
<tag> Synopsis </tag> Pause for a specified number of seconds
<tag> Usage </tag> <tt>sleep (Double_Type n)</tt>
<tag> Description </tag>
  The <tt>sleep</tt> function delays the current process for the
  specified number of seconds.  If it is interrupted by a signal, it
  will return prematurely.
<tag> Notes </tag>
  Not all system support sleeping for a fractional part of a second.
</descrip><p>

<sect><bf>system</bf><label id="system"><p><descrip>
<tag> Synopsis </tag> Execute a shell command
<tag> Usage </tag> <tt>Integer_Type system (String_Type cmd)</tt>
<tag> Description </tag>
  The <tt>system</tt> function may be used to execute the string
  expression <tt>cmd</tt> in an inferior shell.  This function is an
  interface to the C <tt>system</tt> function which returns an
  implementation-defined result.   On Linux, it returns 127 if the
  inferior shell could not be invoked, -1 if there was some other
  error, otherwise it returns the return code for <tt>cmd</tt>.
<tag> Example </tag>
<tscreen><verb>
    define dir ()
    {
       () = system ("DIR");
    }
</verb></tscreen>
  displays a directory listing of the current directory under MSDOS or
  VMS.
<tag> See Also </tag> <tt>popen, listdir</tt>
</descrip><p>

<sect><bf>umask</bf><label id="umask"><p><descrip>
<tag> Synopsis </tag> Set the file creation mask
<tag> Usage </tag> <tt>Int_Type umask (Int_Type m)</tt>
<tag> Description </tag>
  The <tt>umask</tt> function sets the file creation mask to <tt>m</tt> and
  returns the previous mask.
<tag> See Also </tag> <tt>stat_file</tt>
</descrip><p>

<sect><bf>uname</bf><label id="uname"><p><descrip>
<tag> Synopsis </tag> Get the system name
<tag> Usage </tag> <tt>Struct_Tye uname ()</tt>
<tag> Description </tag>
  The <tt>uname</tt> function returns a structure containing information
  about the operating system.  The structure contains the following
  fields:
<tscreen><verb>
       sysname  (Name of the operating system)
       nodename (Name of the node within the network)
       release  (Release level of the OS)
       version  (Current version of the release)
       machine  (Name of the hardware)
</verb></tscreen>
<tag> Notes </tag>
  Not all systems support this function.
<tag> See Also </tag> <tt>getenv, pack, unpack</tt>
</descrip><p>


<chapt>Eval Functions<p>
<sect><bf>autoload</bf><label id="autoload"><p><descrip>
<tag> Synopsis </tag> Load a function from a file
<tag> Usage </tag> <tt>autoload (String_Type funct, String_Type file)</tt>
<tag> Description </tag>
    The <tt>autoload</tt> function is used to declare <tt>funct</tt> to the
    interpreter and indicate that it should be loaded from <tt>file</tt> when
    it is actually used.
<tag> Example </tag>
    Suppose <tt>bessel_j0</tt> is a function defined in the file
    <tt>bessel.sl</tt>.  Then the statement
<tscreen><verb>
      autoload ("bessel_j0", "bessel.sl");
</verb></tscreen>
    will cause <tt>bessel.sl</tt> to be loaded prior to the execution of
    <tt>bessel_j0</tt>
<tag> See Also </tag> <tt>evalfile</tt>
</descrip><p>

<sect><bf>byte_compile_file</bf><label id="byte_compile_file"><p><descrip>
<tag> Synopsis </tag> Compile a file to byte-code for faster loading.
<tag> Usage </tag> <tt>byte_compile_file (String_Type file, Integer_Type method)</tt>
<tag> Description </tag>
  The <tt>byte_compile_file</tt> function byte-compiles <tt>file</tt>
  producing a new file with the same name except a <tt>'c'</tt> is added
  to the output file name.  For example, <tt>file</tt> is
  <tt>"site.sl"</tt>, then the function produces a new file named
  <tt>site.slc</tt>.
<tag> Notes </tag>
  The <tt>method</tt> parameter is not used in the current
  implementation.  Its use is reserved for the future.  For now, set
  it to <tt>0</tt>.
<tag> See Also </tag> <tt>evalfile</tt>
</descrip><p>

<sect><bf>eval</bf><label id="eval"><p><descrip>
<tag> Synopsis </tag> Interpret a string as <bf>S-lang</bf> code
<tag> Usage </tag> <tt>eval (String_Type expression, [,String_Type namespace])</tt>
<tag> Description </tag>
  The <tt>eval</tt> function parses a string as S-Lang code and executes the
  result.  If called with the optional namespace argument, then the
  string will be evaluated in the specified namespace.

  This is a useful function in many contexts such as dynamically
  generating function definitions where there is no way to generate
  them otherwise.
<tag> Example </tag>
<tscreen><verb>
    if (0 == is_defined ("my_function"))
      eval ("define my_function () { message (\"my_function\"); }");
</verb></tscreen>
<tag> See Also </tag> <tt>is_defined, autoload, evalfile</tt>
</descrip><p>

<sect><bf>evalfile</bf><label id="evalfile"><p><descrip>
<tag> Synopsis </tag> Interpret a file containing <bf>S-lang</bf> code.
<tag> Usage </tag> <tt>Integer_Type evalfile (String_Type file, [,String_Type namespace])</tt>
<tag> Description </tag>
  The <tt>evalfile</tt> function loads <tt>file</tt> into the interpreter
  and executes it.  If called with the optional namespace argument,
  the file will be loaded into the specified namespace, which will be
  created if necessary.  If no errors were encountered, <tt>1</tt> will
  be returned; otherwise, a <bf>S-lang</bf> error will be generated and the
  function will return zero.
<tag> Example </tag>
<tscreen><verb>
    define load_file (file)
    {
       ERROR_BLOCK { _clear_error (); }
       () = evalfile (file);
    }
</verb></tscreen>
<tag> Notes </tag>
  For historical reasons, the return value of this function is not
  really useful.
<tag> See Also </tag> <tt>eval, autoload</tt>
</descrip><p>


<chapt>Module Functions<p>
<sect><bf>get_import_module_path</bf><label id="get_import_module_path"><p><descrip>
<tag> Synopsis </tag> Get the search path for dynamically loadable objects
<tag> Usage </tag> <tt>String_Type get_import_module_path ()</tt>
<tag> Description </tag>
  The <tt>get_import_module_path</tt> may be used to get the search path
  for dynamically shared objects.  Such objects may be made accessable
  to the application via the <tt>import</tt> function.
<tag> See Also </tag> <tt>import, set_import_module_path</tt>
</descrip><p>

<sect><bf>import</bf><label id="import"><p><descrip>
<tag> Synopsis </tag> Dynamically link to a specified module
<tag> Usage </tag> <tt>import (String_Type module [, String_Type namespace])</tt>
<tag> Description </tag>
  The <tt>import</tt> function causes the run-time linker to dynamically
  link to the shared object specified by the <tt>module</tt> parameter.
  It seaches for the shared object as follows: First a search is
  performed along all module paths specified by the application.  Then
  a search is made along the paths defined via the
  <tt>set_import_module_path</tt> function.  If not found, a search is
  performed along the paths given by the <tt>SLANG_MODULE_PATH</tt>
  environment variable.  Finally, a system dependent search is
  performed (e.g., using the <tt>LD_LIBRARY_PATH</tt> environment
  variable).

  The optional second parameter may be used to specify a namespace
  for the intrinsic functions and variables of the module.  If this
  parameter is not present, the intrinsic objects will be placed into
  the global namespace.

  This function signals an error if the specified module is not found.
<tag> Notes </tag>
  The <tt>import</tt> function is not available on all systems.
<tag> See Also </tag> <tt>set_import_module_path, use_namespace, current_namespace, getenv, evalfile</tt>
</descrip><p>

<sect><bf>set_import_module_path</bf><label id="set_import_module_path"><p><descrip>
<tag> Synopsis </tag> Set the search path for dynamically loadable objects
<tag> Usage </tag> <tt>set_import_module_path (String_Type path_list)</tt>
<tag> Description </tag>
  The <tt>set_import_module_path</tt> may be used to set the search path
  for dynamically shared objects.  Such objects may be made accessable
  to the application via the <tt>import</tt> function.
  
  The actual syntax for the specification of the set of paths will
  vary according to the operating system.  Under Unix, a colon
  character is used to separate paths in <tt>path_list</tt>.  For win32
  systems a semi-colon is used.
<tag> See Also </tag> <tt>import, get_import_module_path</tt>
</descrip><p>


<chapt>Debugging Functions<p>
<sect><bf>_clear_error</bf><label id="_clear_error"><p><descrip>
<tag> Synopsis </tag> Clear an error condition
<tag> Usage </tag> <tt>_clear_error ()</tt>
<tag> Description </tag>
  This function may be used in error-blocks to clear the error that
  triggered execution of the error block.  Execution resumes following
  the statement, in the scope of the error-block, that triggered the
  error.
<tag> Example </tag>
  Consider the following wrapper around the <tt>putenv</tt> function:
<tscreen><verb>
    define try_putenv (name, value)
    {
       variable status;
       ERROR_BLOCK
        {
          _clear_error ();
          status = -1;
        }
       status = 0;
       putenv (sprintf ("%s=%s", name, value);
       return status;
    }
</verb></tscreen>
  If <tt>putenv</tt> fails, it generates an error condition, which the
  <tt>try_putenv</tt> function catches and clears.  Thus <tt>try_putenv</tt>
  is a function that returns <tt>-1</tt> upon failure and <tt>0</tt> upon
  success.
<tag> See Also </tag> <tt>_trace_function, _slangtrace, _traceback</tt>
</descrip><p>

<sect><bf>_debug_info</bf><label id="_debug_info"><p><descrip>
<tag> Synopsis </tag> Configure debugging information
<tag> Usage </tag> <tt>Integer_Type _debug_info</tt>
<tag> Description </tag>
  The <tt>_debug_info</tt> variable controls whether or not extra code
  should be generated for additional debugging and traceback
  information.  Currently, if <tt>_debug_info</tt> is zero, no extra code
  will be generated; otherwise extra code will be inserted into the
  compiled bytecode for additional debugging data.

  The value of this variable is is local to each compilation unit and
  setting its value in one unit has no effect upon its value in other
  units.
<tag> Example </tag>
<tscreen><verb>
    _debug_info = 1;   % Enable debugging information
</verb></tscreen>
<tag> Notes </tag>
  Setting this variable to a non-zero value may slow down the
  interpreter somewhat.
<tag> See Also </tag> <tt>_traceback, _slangtrace</tt>
</descrip><p>

<sect><bf>_slangtrace</bf><label id="_slangtrace"><p><descrip>
<tag> Synopsis </tag> Turn function tracing on or off.
<tag> Usage </tag> <tt>Integer_Type _slangtrace</tt>
<tag> Description </tag>
  The <tt>_slangtrace</tt> variable is a debugging aid that when set to a
  non-zero value enables tracing when function declared by
  <tt>_trace_function</tt> is entered.  If the value is greater than
  zero, both intrinsic and user defined functions will get traced.
  However, if set to a value less than zero, intrinsic functions will
  not get traced.
<tag> See Also </tag> <tt>_trace_function, _traceback, _print_stack</tt>
</descrip><p>

<sect><bf>_trace_function</bf><label id="_trace_function"><p><descrip>
<tag> Synopsis </tag> Set the function to trace
<tag> Usage </tag> <tt>_trace_function (String_Type f)</tt>
<tag> Description </tag>
  <tt>_trace_function</tt> declares that the <bf>S-lang</bf> function with name
  <tt>f</tt> is to be traced when it is called.  Calling
  <tt>_trace_function</tt> does not in itself turn tracing on.  Tracing
  is turned on only when the variable <tt>_slangtrace</tt> is non-zero.
<tag> See Also </tag> <tt>_slangtrace, _traceback</tt>
</descrip><p>

<sect><bf>_traceback</bf><label id="_traceback"><p><descrip>
<tag> Synopsis </tag> Generate a traceback upon error
<tag> Usage </tag> <tt>Integer_Type _traceback</tt>
<tag> Description </tag>
  <tt>_traceback</tt> is an intrinsic integer variable whose value
  controls whether or not a traceback of the call stack is to be
  generated upon error.  If <tt>_traceback</tt> is greater than zero, a
  full traceback will be generated, which includes the values of local
  variables.  If the value is less than zero, a traceback will be
  generated without local variable information, and if
  <tt>_traceback</tt> is zero the traceback will not be generated.

  Local variables are represented in the form <tt>$n</tt> where <tt>n</tt> is an
  integer numbered from zero.  More explicitly, <tt>$0</tt> represents the
  first local variable, <tt>$1</tt> represents the second, and so on.
  Please note that function parameters are local variables and that the
  first parameter corresponds to <tt>$0</tt>.
<tag> See Also </tag> <tt>_slangtrace, error</tt>
</descrip><p>


<chapt>Stack Functions<p>
<sect><bf>__pop_args</bf><label id="__pop_args"><p><descrip>
<tag> Synopsis </tag> Remove n function arguments from the stack
<tag> Usage </tag> <tt>variable args = __pop_args(Integer_Type n);</tt>
<tag> Description </tag>
  This function together with the companion function <tt>__push_args</tt>
  is useful for passing the arguments of a function to another function.
  <tt>__pop_args</tt> returns an array of <tt>n</tt> structures with a
  single structure field called <tt>value</tt>, which represents the value
  of the argument.
<tag> Example </tag>
  Consider the following <tt>print</tt> function.  It prints all its
  arguments to <tt>stdout</tt> separated by spaces:
<tscreen><verb>
    define print ()
    {
       variable i;
       variable args = __pop_args (_NARGS);
   
       for (i = 0; i &lt; _NARGS; i++)
         {
            () = fputs (string (args[i].value), stdout);
            () = fputs (" ", stdout);
         }
       () = fputs ("\n", stdout);
       () = fflush (stdout);
    }
</verb></tscreen>
  Now consider the problem of defining a function called <tt>ones</tt>
  that returns a multi-dimensional array with all the elements set to
  1.  For example, <tt>ones(10)</tt> should return a 1-d array of ones,
  whereas <tt>ones(10,20)</tt> should return a 10x20 array.
<tscreen><verb>
    define ones ()
    {
      !if (_NARGS) return 1;
      variable a;
   
      a = __pop_args (_NARGS);
      return @Array_Type (Integer_Type, [__push_args (a)]) + 1;
    }
</verb></tscreen>
  Here, <tt>__push_args</tt> was used to push on the arguments passed to
  the <tt>ones</tt> function onto the stack to be used when dereferencing
  <tt>Array_Type</tt>.
<tag> See Also </tag> <tt>__push_args, typeof, _pop_n</tt>
</descrip><p>

<sect><bf>__push_args</bf><label id="__push_args"><p><descrip>
<tag> Synopsis </tag> Remove n function arguments onto the stack
<tag> Usage </tag> <tt>__push_args (Struct_Type args);</tt>
<tag> Description </tag>
  This function together with the companion function <tt>__pop_args</tt>
  is useful for passing the arguments of one function to another.
  See the desription of <tt>__pop_args</tt> for more information.
<tag> See Also </tag> <tt>__pop_args, typeof, _pop_n</tt>
</descrip><p>

<sect><bf>_pop_n</bf><label id="_pop_n"><p><descrip>
<tag> Synopsis </tag> Remove objects from the stack
<tag> Usage </tag> <tt>_pop_n (Integer_Type n);</tt>
<tag> Description </tag>
  The <tt>_pop_n</tt> function pops <tt>n</tt> objects from the top of the
  stack.
<tag> Example </tag>
<tscreen><verb>
    define add3 ()
    {
       variable x, y, z;
       if (_NARGS != 3)
         {
            _pop_n (_NARGS);
            error ("add3: Expecting 3 arguments");
         }
       (x, y, z) = ();
       return x + y + z;
    }
</verb></tscreen>
<tag> See Also </tag> <tt>_stkdepth, pop</tt>
</descrip><p>

<sect><bf>_print_stack</bf><label id="_print_stack"><p><descrip>
<tag> Synopsis </tag> print the values on the stack.
<tag> Usage </tag> <tt>_print_stack ()</tt>
<tag> Description </tag>
  This function dumps out what is currently on the <bf>S-lang</bf>.  It does not
  alter the stack and it is usually used for debugging purposes.
<tag> See Also </tag> <tt>_stkdepth, string</tt>
</descrip><p>

<sect><bf>_stk_reverse</bf><label id="_stk_reverse"><p><descrip>
<tag> Synopsis </tag> Reverse the order of the objects on the stack.
<tag> Usage </tag> <tt>_stk_reverse (Integer_Type n)</tt>
<tag> Description </tag>
   The <tt>_stk_reverse</tt> function reverses the order of the top
   <tt>n</tt> items on the stack.
<tag> See Also </tag> <tt>_stkdepth, _stk_roll</tt>
</descrip><p>

<sect><bf>_stk_roll</bf><label id="_stk_roll"><p><descrip>
<tag> Synopsis </tag> Roll items on the stack
<tag> Usage </tag> <tt>_stk_roll (Integer_Type n);</tt>
<tag> Description </tag>
  This function may be used to alter the arrangement of objects on the
  stack.  Specifically, if the integer <tt>n</tt> is positive, the top
  <tt>n</tt> items on the stack are rotated up.  If
  <tt>n</tt> is negative, the top <tt>abs(n)</tt> items on the stack are
  rotated down.
<tag> Example </tag>
  If the stack looks like:
<tscreen><verb>
    item-0
    item-1
    item-2
    item-3
</verb></tscreen>
  where <tt>item-0</tt> is at the top of the stack, then
  <tt>_stk_roll(-3)</tt> will change the stack to:
<tscreen><verb>
    item-2
    item-0
    item-1
    item-3
</verb></tscreen>
<tag> Notes </tag>
  This function only has an effect for <tt>abs(n) &gt; 1</tt>.
<tag> See Also </tag> <tt>_stkdepth, _stk_reverse, _pop_n, _print_stack</tt>
</descrip><p>

<sect><bf>_stkdepth</bf><label id="_stkdepth"><p><descrip>
<tag> Usage </tag> <tt>Get the number of objects currently on the stack.</tt>
<tag> Synopsis </tag> Integer_Type _stkdepth ()
<tag> Description </tag>
  The <tt>_stkdepth</tt> function returns number of items on stack prior
  to the call of <tt>_stkdepth</tt>.
<tag> See Also </tag> <tt>_print_stack, _stk_reverse, _stk_roll</tt>
</descrip><p>

<sect><bf>dup</bf><label id="dup"><p><descrip>
<tag> Synopsis </tag> Duplicate the value at the top of the stack
<tag> Usage </tag> <tt>dup ()</tt>
<tag> Description </tag>
  This function returns an exact duplicate of the object on top of the
  stack.  For some objects such as arrays or structures, it creates a
  new reference to the array.  However, for simple scalar S-Lang types such
  as strings, integers, and doubles, it creates a new copy of the
  object.
<tag> See Also </tag> <tt>pop, typeof</tt>
</descrip><p>

<sect><bf>exch</bf><label id="exch"><p><descrip>
<tag> Synopsis </tag> Exchange two items on the stack
<tag> Usage </tag> <tt>exch ()</tt>
<tag> Description </tag>
  The <tt>exch</tt> swaps the two top items on the stack.
<tag> See Also </tag> <tt>pop, _stk_reverse, _stk_roll</tt>
</descrip><p>

<sect><bf>pop</bf><label id="pop"><p><descrip>
<tag> Synopsis </tag> Discard an item from the stack
<tag> Usage </tag> <tt>pop ()</tt>
<tag> Description </tag>
  The <tt>pop</tt> function removes the top item from the stack.
<tag> See Also </tag> <tt>_pop_n</tt>
</descrip><p>


<chapt>Miscellaneous Functions<p>
<sect><bf>__class_id</bf><label id="__class_id"><p><descrip>
<tag> Synopsis </tag> Return the class-id of a specified type
<tag> Usage </tag> <tt>Int_Type __class_id (DataType_Type type))</tt>
<tag> Description </tag>
  This function returns the internal class-id of a specified data type.
<tag> See Also </tag> <tt>typeof, _typeof, __class_type</tt>
</descrip><p>

<sect><bf>__class_type</bf><label id="__class_type"><p><descrip>
<tag> Synopsis </tag> Return the class-type of a specified type
<tag> Usage </tag> <tt>Int_Type __class_type (DataType_Type type))</tt>
<tag> Description </tag>
  Internally <bf>S-lang</bf> objects are classified according to four types:
  scalar, vector, pointer, and memory managed types.  For example, an
  integer is implemented as a scalar, a complex number as a vector,
  and a string is represented as a pointer.  The <tt>__class_type</tt>
  function returns an integer representing the class-type associated
  with the specified data type. Specifically, it returns:
<tscreen><verb>
       0    memory-managed
       1    scalar
       2    vector
       3    pointer
</verb></tscreen>
<tag> See Also </tag> <tt>typeof, _typeof, __class_id</tt>
</descrip><p>

<sect><bf>__eqs</bf><label id="__eqs"><p><descrip>
<tag> Synopsis </tag> Test for equality between two objects
<tag> Usage </tag> <tt>Int_Type __eqs (a, b)</tt>
<tag> Description </tag>
  This function tests its two arguments for equalit and returns <tt>1</tt>
  if they are equal, and <tt>0</tt> otherwise.  To be equal, the data type of
  the arguments must match and the values of the objects must
  reference the same underlying object.
<tag> Example </tag>
   __eqs (1, 1)         ===&gt; 1
   __eqs (1, 1.0)       ===&gt; 0
   __eqs ("a", 1)       ===&gt; 0
   __eqs ([1,2], [1,2]) ===&gt; 0
<tag> See Also </tag> <tt>typeof, __get_reference</tt>
<tag> Notes </tag>
   This function should be thought of as a test for "sameness".
</descrip><p>

<sect><bf>__get_reference</bf><label id="__get_reference"><p><descrip>
<tag> Synopsis </tag> Get a reference to a global object
<tag> Usage </tag> <tt>Ref_Type __get_reference (String_Type nm)</tt>
<tag> Description </tag>
  This function returns a reference to a global variable or function
  whose name is specified by <tt>nm</tt>.  If no such object exists, it
  returns <tt>NULL</tt>, otherwise it returns a reference.
<tag> Example </tag>
   For example, consider the function:
<tscreen><verb>
    define runhooks (hook)
    {
       variable f;
       f = __get_reference (hook);
       if (f != NULL)
         @f ();
    }
</verb></tscreen>
   This function could be called from another <bf>S-lang</bf> function to
   allow customization of that function, e.g., if the function
   represents a mode, the hook could be called to setup keybindings
   for the mode.
<tag> See Also </tag> <tt>is_defined, typeof, eval, autoload, __is_initialized, __uninitialize</tt>
</descrip><p>

<sect><bf>__uninitialize</bf><label id="__uninitialize"><p><descrip>
<tag> Synopsis </tag> Uninitialize a variable
<tag> Usage </tag> <tt>__uninitialize (Ref_Type x)</tt>
<tag> Description </tag>
  The <tt>__uninitialize</tt> function may be used to uninitialize the
  variable referenced by the parameter <tt>x</tt>.
<tag> Example </tag>
  The following two lines are equivalent:
<tscreen><verb>
     () = __tmp(z);
     __uninitialize (&amp;z);
</verb></tscreen>
<tag> See Also </tag> <tt>__tmp, __is_initialized</tt>
</descrip><p>

<sect><bf>_auto_declare</bf><label id="_auto_declare"><p><descrip>
<tag> Synopsis </tag> Set automatic variable declaration mode
<tag> Usage </tag> <tt>Integer_Type _auto_declare</tt>
<tag> Description </tag>
  The <tt>_auto_declare</tt> may be used to have all undefined variables
  implicitely declared as <tt>static</tt>.  If set to zero, any variable
  must be declared witha <tt>variable</tt> declaration before it can be
  used.  If set to one, then any undeclared variabled will be declared
  as a <tt>static</tt> global variable.

  The <tt>_auto_declare</tt> variable is is local to each compilation unit and
  setting its value in one unit has no effect upon its value in other
  units.   The value of this variable has no effect upon the variables
  in a function.
<tag> Example </tag>
  The following code will not compile if <tt>X</tt> not been
  declared:
<tscreen><verb>
    X = 1;
</verb></tscreen>
  However, 
<tscreen><verb>
    _auto_declare = 1;   % declare variables as static.
    X = 1;
</verb></tscreen>
  is equivalent to 
<tscreen><verb>
    static variable X = 1;
</verb></tscreen>
<tag> Notes </tag>
  This variable should be used sparingly and is intended primarily for
  interactive applications where one types <bf>S-lang</bf> commands at a prompt.
</descrip><p>

<sect><bf>current_namespace</bf><label id="current_namespace"><p><descrip>
<tag> Synopsis </tag> Get the name of the current namespace
<tag> Usage </tag> <tt>String_Type current_namespace ()</tt>
<tag> Description </tag>
   The <tt>current_namespace</tt> function returns the name of the
   current namespace.  If the current namespace is anonymous, that is,
   has not been given a name via the <tt>implements</tt> function, the
   empty string <tt>""</tt> will be returned.
<tag> See Also </tag> <tt>implements, use_namespace, import</tt>
</descrip><p>

<sect><bf>getenv</bf><label id="getenv"><p><descrip>
<tag> Synopsis </tag> Get the value of an environment variable
<tag> Usage </tag> <tt>String_Type getenv(String_Type var)</tt>
<tag> Description </tag>
   The <tt>getenv</tt> function returns a string that represents the
   value of an environment variable <tt>var</tt>.  It will return
   <tt>NULL</tt> if there is no environment variable whose name is given
   by <tt>var</tt>.
<tag> Example </tag>
<tscreen><verb>
    if (NULL != getenv ("USE_COLOR"))
      {
        set_color ("normal", "white", "blue");
        set_color ("status", "black", "gray");
        USE_ANSI_COLORS = 1;
      }
</verb></tscreen>
<tag> See Also </tag> <tt>putenv, strlen, is_defined</tt>
</descrip><p>

<sect><bf>implements</bf><label id="implements"><p><descrip>
<tag> Synopsis </tag> Name a private namespace
<tag> Usage </tag> <tt>implements (String_Type name);</tt>
<tag> Description </tag>
  The <tt>implements</tt> function may be used to name the private
  namespace associated with the current compilation unit.  Doing so
  will enable access to the members of the namespace from outside the
  unit.  The name of the global namespace is <tt>Global</tt>.
<tag> Example </tag>
  Suppose that some file <tt>t.sl</tt> contains:
<tscreen><verb>
     implements ("Ts_Private");
     static define message (x)
     {
        Global-&gt;vmessage ("Ts_Private message: %s", x);
     }
     message ("hello");
</verb></tscreen>
  will produce <tt>"Ts_Private message: hello"</tt>.  This <tt>message</tt>
  function may be accessed from outside via:
<tscreen><verb>
    Ts_Private-&gt;message ("hi");
</verb></tscreen>
<tag> Notes </tag>
  Since <tt>message</tt> is an intrinsic function, it is global and may
  not be redefined in the global namespace.
<tag> See Also </tag> <tt>use_namespace, current_namespace, import</tt>
</descrip><p>

<sect><bf>putenv</bf><label id="putenv"><p><descrip>
<tag> Synopsis </tag> Add or change an environment variable
<tag> Usage </tag> <tt>putenv (String_Type s)</tt>
<tag> Description </tag>
    This functions adds string <tt>s</tt> to the environment.  Typically,
    <tt>s</tt> should of the form <tt>"name=value"</tt>.  The function
    signals a <bf>S-lang</bf> error upon failure.
<tag> Notes </tag>
    This function is not available on all systems.
<tag> See Also </tag> <tt>getenv, sprintf</tt>
</descrip><p>

<sect><bf>use_namespace</bf><label id="use_namespace"><p><descrip>
<tag> Synopsis </tag> Change to another namespace
<tag> Usage </tag> <tt>use_namespace (String_Type name)</tt>
<tag> Description </tag>
   The <tt>use_namespace</tt> function changes the current namespace to
   the one specified by the parameter.  If the specified namespace
   does not exist, an error will be generated.
<tag> See Also </tag> <tt>implements, current_namespace, import</tt>
</descrip><p>


</book>
