This is Info file gcc.info, produced by Makeinfo version 1.68 from the
input file ../../gcc/gcc.texi.

INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU C compiler.
END-INFO-DIR-ENTRY
   This file documents the use and the internals of the GNU compiler.

   Published by the Free Software Foundation 59 Temple Place - Suite 330
Boston, MA 02111-1307 USA

   Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998
Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the sections entitled "GNU General Public License" and "Funding
for Free Software" are included exactly as in the original, and
provided that the entire resulting derived work is distributed under
the terms of a permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the sections entitled "GNU General Public
License" and "Funding for Free Software", and this permission notice,
may be included in translations approved by the Free Software Foundation
instead of in the original English.


File: gcc.info,  Node: C++ Dialect Options,  Next: Warning Options,  Prev: C Dialect Options,  Up: Invoking GCC

Options Controlling C++ Dialect
===============================

   This section describes the command-line options that are only
meaningful for C++ programs; but you can also use most of the GNU
compiler options regardless of what language your program is in.  For
example, you might compile a file `firstClass.C' like this:

     g++ -g -felide-constructors -O -c firstClass.C

In this example, only `-felide-constructors' is an option meant only
for C++ programs; you can use the other options with any language
supported by GNU CC.

   Here is a list of options that are *only* for compiling C++ programs:

`-fno-access-control'
     Turn off all access checking.  This switch is mainly useful for
     working around bugs in the access control code.

`-fall-virtual'
     Treat all possible member functions as virtual, implicitly.  All
     member functions (except for constructor functions and `new' or
     `delete' member operators) are treated as virtual functions of the
     class where they appear.

     This does not mean that all calls to these member functions will
     be made through the internal table of virtual functions.  Under
     some circumstances, the compiler can determine that a call to a
     given virtual function can be made directly; in these cases the
     calls are direct in any case.

`-fcheck-new'
     Check that the pointer returned by `operator new' is non-null
     before attempting to modify the storage allocated.  The current
     Working Paper requires that `operator new' never return a null
     pointer, so this check is normally unnecessary.

`-fconserve-space'
     Put uninitialized or runtime-initialized global variables into the
     common segment, as C does.  This saves space in the executable at
     the cost of not diagnosing duplicate definitions.  If you compile
     with this flag and your program mysteriously crashes after
     `main()' has completed, you may have an object that is being
     destroyed twice because two definitions were merged.

`-fdollars-in-identifiers'
     Accept `$' in identifiers.  You can also explicitly prohibit use of
     `$' with the option `-fno-dollars-in-identifiers'.  (GNU C allows
     `$' by default on most target systems, but there are a few
     exceptions.)  Traditional C allowed the character `$' to form part
     of identifiers.  However, ANSI C and C++ forbid `$' in identifiers.

`-fenum-int-equiv'
     Anachronistically permit implicit conversion of `int' to
     enumeration types.  Current C++ allows conversion of `enum' to
     `int', but not the other way around.

`-fexternal-templates'
     Cause template instantiations to obey `#pragma interface' and
     `implementation'; template instances are emitted or not according
     to the location of the template definition.  *Note Template
     Instantiation::, for more information.

     This option is deprecated.

`-falt-external-templates'
     Similar to -fexternal-templates, but template instances are
     emitted or not according to the place where they are first
     instantiated.  *Note Template Instantiation::, for more
     information.

     This option is deprecated.

`-ffor-scope'
`-fno-for-scope'
     If -ffor-scope is specified, the scope of variables declared in a
     for-init-statement is limited to the `for' loop itself, as
     specified by the draft C++ standard.  If -fno-for-scope is
     specified, the scope of variables declared in a for-init-statement
     extends to the end of the enclosing scope, as was the case in old
     versions of gcc, and other (traditional) implementations of C++.

     The default if neither flag is given to follow the standard, but
     to allow and give a warning for old-style code that would
     otherwise be invalid, or have different behavior.

`-fno-gnu-keywords'
     Do not recognize `classof', `headof', `signature', `sigof' or
     `typeof' as a keyword, so that code can use these words as
     identifiers.  You can use the keywords `__classof__',
     `__headof__', `__signature__', `__sigof__', and `__typeof__'
     instead.  `-ansi' implies `-fno-gnu-keywords'.

`-fguiding-decls'
     Treat a function declaration with the same type as a potential
     function template instantiation as though it declares that
     instantiation, not a normal function.  If a definition is given
     for the function later in the translation unit (or another
     translation unit if the target supports weak symbols), that
     definition will be used; otherwise the template will be
     instantiated.  This behavior reflects the C++ language prior to
     September 1996, when guiding declarations were removed.

     This option implies `-fname-mangling-version-0', and will not work
     with other name mangling versions.

`-fno-implicit-templates'
     Never emit code for templates which are instantiated implicitly
     (i.e. by use); only emit code for explicit instantiations.  *Note
     Template Instantiation::, for more information.

`-fhandle-signatures'
     Recognize the `signature' and `sigof' keywords for specifying
     abstract types.  The default (`-fno-handle-signatures') is not to
     recognize them.  *Note Type Abstraction using Signatures: C++
     Signatures.

`-fhuge-objects'
     Support virtual function calls for objects that exceed the size
     representable by a `short int'.  Users should not use this flag by
     default; if you need to use it, the compiler will tell you so.  If
     you compile any of your code with this flag, you must compile
     *all* of your code with this flag (including the C++ library, if
     you use it).

     This flag is not useful when compiling with -fvtable-thunks.

`-fno-implement-inlines'
     To save space, do not emit out-of-line copies of inline functions
     controlled by `#pragma implementation'.  This will cause linker
     errors if these functions are not inlined everywhere they are
     called.

`-fmemoize-lookups'
`-fsave-memoized'
     Use heuristics to compile faster.  These heuristics are not
     enabled by default, since they are only effective for certain
     input files.  Other input files compile more slowly.

     The first time the compiler must build a call to a member function
     (or reference to a data member), it must (1) determine whether the
     class implements member functions of that name; (2) resolve which
     member function to call (which involves figuring out what sorts of
     type conversions need to be made); and (3) check the visibility of
     the member function to the caller.  All of this adds up to slower
     compilation.  Normally, the second time a call is made to that
     member function (or reference to that data member), it must go
     through the same lengthy process again.  This means that code like
     this:

          cout << "This " << p << " has " << n << " legs.\n";

     makes six passes through all three steps.  By using a software
     cache, a "hit" significantly reduces this cost.  Unfortunately,
     using the cache introduces another layer of mechanisms which must
     be implemented, and so incurs its own overhead.
     `-fmemoize-lookups' enables the software cache.

     Because access privileges (visibility) to members and member
     functions may differ from one function context to the next, G++
     may need to flush the cache.  With the `-fmemoize-lookups' flag,
     the cache is flushed after every function that is compiled.  The
     `-fsave-memoized' flag enables the same software cache, but when
     the compiler determines that the context of the last function
     compiled would yield the same access privileges of the next
     function to compile, it preserves the cache.  This is most helpful
     when defining many member functions for the same class: with the
     exception of member functions which are friends of other classes,
     each member function has exactly the same access privileges as
     every other, and the cache need not be flushed.

     The code that implements these flags has rotted; you should
     probably avoid using them.

`-fstrict-prototype'
     Within an `extern "C"' linkage specification, treat a function
     declaration with no arguments, such as `int foo ();', as declaring
     the function to take no arguments.  Normally, such a declaration
     means that the function `foo' can take any combination of
     arguments, as in C.  `-pedantic' implies `-fstrict-prototype'
     unless overridden with `-fno-strict-prototype'.

     This flag no longer affects declarations with C++ linkage.

`-fname-mangling-version-N'
     Control the way in which names are mangled.  Version 0 is
     compatible with versions of g++ before 2.8.  Version 1 is the
     default.  Version 1 will allow correct mangling of function
     templates.  For example, version 0 mangling does not mangle
     foo<int, double> and foo<int, char> given this declaration:

          template <class T, class U> void foo(T t);

`-fno-nonnull-objects'
     Don't assume that a reference is initialized to refer to a valid
     object.  Although the current C++ Working Paper prohibits null
     references, some old code may rely on them, and you can use
     `-fno-nonnull-objects' to turn on checking.

     At the moment, the compiler only does this checking for
     conversions to virtual base classes.

`-foperator-names'
     Recognize the operator name keywords `and', `bitand', `bitor',
     `compl', `not', `or' and `xor' as synonyms for the symbols they
     refer to.  `-ansi' implies `-foperator-names'.

`-fno-optional-diags'
     Disable diagnostics that the standard says a compiler does not
     need to issue.  Currently, this means the diagnostic for a name
     having multiple meanings within a class.

`-frepo'
     Enable automatic template instantiation.  This option also implies
     `-fno-implicit-templates'.  *Note Template Instantiation::, for
     more information.

`-fsquangle'
`-fno-squangle'
     `-fsquangle' will enable a compressed form of name mangling for
     identifiers. In particular, it helps to shorten very long names by
     recognizing types and class names which occur more than once,
     replacing them with special short ID codes.  This option also
     requires any C++ libraries being used to be compiled with this
     option as well.  The compiler has this disabled (the equivalent of
     `-fno-squangle') by default.

`-fthis-is-variable'
     Permit assignment to `this'.  The incorporation of user-defined
     free store management into C++ has made assignment to `this' an
     anachronism.  Therefore, by default it is invalid to assign to
     `this' within a class member function; that is, GNU C++ treats
     `this' in a member function of class `X' as a non-lvalue of type
     `X *'.  However, for backwards compatibility, you can make it
     valid with `-fthis-is-variable'.

`-fvtable-thunks'
     Use `thunks' to implement the virtual function dispatch table
     (`vtable').  The traditional (cfront-style) approach to
     implementing vtables was to store a pointer to the function and two
     offsets for adjusting the `this' pointer at the call site.  Newer
     implementations store a single pointer to a `thunk' function which
     does any necessary adjustment and then calls the target function.

     This option also enables a heuristic for controlling emission of
     vtables; if a class has any non-inline virtual functions, the
     vtable will be emitted in the translation unit containing the
     first one of those.

`-ftemplate-depth-N'
     Set the maximum instantiation depth for template classes to N.  A
     limit on the template instantiation depth is needed to detect
     endless recursions during template class instantiation. ANSI/ISO
     C++ conforming programs must not rely on a maximum depth greater
     than 17.

`-nostdinc++'
     Do not search for header files in the standard directories
     specific to C++, but do still search the other standard
     directories.  (This option is used when building the C++ library.)

`-traditional'
     For C++ programs (in addition to the effects that apply to both C
     and C++), this has the same effect as `-fthis-is-variable'.  *Note
     Options Controlling C Dialect: C Dialect Options.

   In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:

`-fno-default-inline'
     Do not assume `inline' for functions defined inside a class scope.
     *Note Options That Control Optimization: Optimize Options.

`-Wold-style-cast'
`-Woverloaded-virtual'
`-Wtemplate-debugging'
     Warnings that apply only to C++ programs.  *Note Options to
     Request or Suppress Warnings: Warning Options.

`-Weffc++'
     Warn about violation of some style rules from Effective C++ by
     Scott Myers.

`+eN'
     Control how virtual function definitions are used, in a fashion
     compatible with `cfront' 1.x.  *Note Options for Code Generation
     Conventions: Code Gen Options.


File: gcc.info,  Node: Warning Options,  Next: Debugging Options,  Prev: C++ Dialect Options,  Up: Invoking GCC

Options to Request or Suppress Warnings
=======================================

   Warnings are diagnostic messages that report constructions which are
not inherently erroneous but which are risky or suggest there may have
been an error.

   You can request many specific warnings with options beginning `-W',
for example `-Wimplicit' to request warnings on implicit declarations.
Each of these specific warning options also has a negative form
beginning `-Wno-' to turn off warnings; for example, `-Wno-implicit'.
This manual lists only one of the two forms, whichever is not the
default.

   These options control the amount and kinds of warnings produced by
GNU CC:

`-fsyntax-only'
     Check the code for syntax errors, but don't do anything beyond
     that.

`-pedantic'
     Issue all the warnings demanded by strict ANSI C and ISO C++;
     reject all programs that use forbidden extensions.

     Valid ANSI C and ISO C++ programs should compile properly with or
     without this option (though a rare few will require `-ansi').
     However, without this option, certain GNU extensions and
     traditional C and C++ features are supported as well.  With this
     option, they are rejected.

     `-pedantic' does not cause warning messages for use of the
     alternate keywords whose names begin and end with `__'.  Pedantic
     warnings are also disabled in the expression that follows
     `__extension__'.  However, only system header files should use
     these escape routes; application programs should avoid them.
     *Note Alternate Keywords::.

     This option is not intended to be useful; it exists only to satisfy
     pedants who would otherwise claim that GNU CC fails to support the
     ANSI standard.

     Some users try to use `-pedantic' to check programs for strict ANSI
     C conformance.  They soon find that it does not do quite what they
     want: it finds some non-ANSI practices, but not all--only those
     for which ANSI C *requires* a diagnostic.

     A feature to report any failure to conform to ANSI C might be
     useful in some instances, but would require considerable
     additional work and would be quite different from `-pedantic'.  We
     recommend, rather, that users take advantage of the extensions of
     GNU C and disregard the limitations of other compilers.  Aside
     from certain supercomputers and obsolete small machines, there is
     less and less reason ever to use any other C compiler other than
     for bootstrapping GNU CC.

`-pedantic-errors'
     Like `-pedantic', except that errors are produced rather than
     warnings.

`-w'
     Inhibit all warning messages.

`-Wno-import'
     Inhibit warning messages about the use of `#import'.

`-Wchar-subscripts'
     Warn if an array subscript has type `char'.  This is a common cause
     of error, as programmers often forget that this type is signed on
     some machines.

`-Wcomment'
     Warn whenever a comment-start sequence `/*' appears in a `/*'
     comment, or whenever a Backslash-Newline appears in a `//' comment.

`-Wformat'
     Check calls to `printf' and `scanf', etc., to make sure that the
     arguments supplied have types appropriate to the format string
     specified.

`-Wimplicit-int'
     Warn when a declaration does not specify a type.

`-Wimplicit-function-declaration'
`-Werror-implicit-function-declaration'
     Give a warning (or error) whenever a function is used before being
     declared.

`-Wimplicit'
     Same as `-Wimplicit-int' and `-Wimplicit-function-'
     `declaration'.

`-Wmain'
     Warn if the type of `main' is suspicious.  `main' should be a
     function with external linkage, returning int, taking either zero
     arguments, two, or three arguments of appropriate types.

`-Wmultichar'
     Warn if a multicharacter constant (`'FOOF'') is used.  Usually they
     indicate a typo in the user's code, as they have
     implementation-defined values, and should not be used in portable
     code.

`-Wparentheses'
     Warn if parentheses are omitted in certain contexts, such as when
     there is an assignment in a context where a truth value is
     expected, or when operators are nested whose precedence people
     often get confused about.

     Also warn about constructions where there may be confusion to which
     `if' statement an `else' branch belongs.  Here is an example of
     such a case:

          {
            if (a)
              if (b)
                foo ();
            else
              bar ();
          }

     In C, every `else' branch belongs to the innermost possible `if'
     statement, which in this example is `if (b)'.  This is often not
     what the programmer expected, as illustrated in the above example
     by indentation the programmer chose.  When there is the potential
     for this confusion, GNU C will issue a warning when this flag is
     specified.  To eliminate the warning, add explicit braces around
     the innermost `if' statement so there is no way the `else' could
     belong to the enclosing `if'.  The resulting code would look like
     this:

          {
            if (a)
              {
                if (b)
                  foo ();
                else
                  bar ();
              }
          }

`-Wreturn-type'
     Warn whenever a function is defined with a return-type that
     defaults to `int'.  Also warn about any `return' statement with no
     return-value in a function whose return-type is not `void'.

`-Wswitch'
     Warn whenever a `switch' statement has an index of enumeral type
     and lacks a `case' for one or more of the named codes of that
     enumeration.  (The presence of a `default' label prevents this
     warning.)  `case' labels outside the enumeration range also
     provoke warnings when this option is used.

`-Wtrigraphs'
     Warn if any trigraphs are encountered (assuming they are enabled).

`-Wunused'
     Warn whenever a variable is unused aside from its declaration,
     whenever a function is declared static but never defined, whenever
     a label is declared but not used, and whenever a statement
     computes a result that is explicitly not used.

     In order to get a warning about an unused function parameter, you
     must specify both `-W' and `-Wunused'.

     To suppress this warning for an expression, simply cast it to
     void.  For unused variables and parameters, use the `unused'
     attribute (*note Variable Attributes::.).

`-Wuninitialized'
     An automatic variable is used without first being initialized.

     These warnings are possible only in optimizing compilation,
     because they require data flow information that is computed only
     when optimizing.  If you don't specify `-O', you simply won't get
     these warnings.

     These warnings occur only for variables that are candidates for
     register allocation.  Therefore, they do not occur for a variable
     that is declared `volatile', or whose address is taken, or whose
     size is other than 1, 2, 4 or 8 bytes.  Also, they do not occur for
     structures, unions or arrays, even when they are in registers.

     Note that there may be no warning about a variable that is used
     only to compute a value that itself is never used, because such
     computations may be deleted by data flow analysis before the
     warnings are printed.

     These warnings are made optional because GNU CC is not smart
     enough to see all the reasons why the code might be correct
     despite appearing to have an error.  Here is one example of how
     this can happen:

          {
            int x;
            switch (y)
              {
              case 1: x = 1;
                break;
              case 2: x = 4;
                break;
              case 3: x = 5;
              }
            foo (x);
          }

     If the value of `y' is always 1, 2 or 3, then `x' is always
     initialized, but GNU CC doesn't know this.  Here is another common
     case:

          {
            int save_y;
            if (change_y) save_y = y, y = new_y;
            ...
            if (change_y) y = save_y;
          }

     This has no bug because `save_y' is used only if it is set.

     Some spurious warnings can be avoided if you declare all the
     functions you use that never return as `noreturn'.  *Note Function
     Attributes::.

`-Wreorder (C++ only)'
     Warn when the order of member initializers given in the code does
     not match the order in which they must be executed.  For instance:

          struct A {
            int i;
            int j;
            A(): j (0), i (1) { }
          };

     Here the compiler will warn that the member initializers for `i'
     and `j' will be rearranged to match the declaration order of the
     members.

`-Wtemplate-debugging'
     When using templates in a C++ program, warn if debugging is not yet
     fully available (C++ only).

`-Wunknown-pragmas'
     Warn when a #pragma directive is encountered which is not
     understood by GCC.  If this command line option is used, warnings
     will even be issued for unknown pragmas in system header files.
     This is not the case if the warnings were only enabled by the
     `-Wall' command line option.

`-Wall'
     All of the above `-W' options combined.  This enables all the
     warnings about constructions that some users consider
     questionable, and that are easy to avoid (or modify to prevent the
     warning), even in conjunction with macros.

   The following `-W...' options are not implied by `-Wall'.  Some of
them warn about constructions that users generally do not consider
questionable, but which occasionally you might wish to check for;
others warn about constructions that are necessary or hard to avoid in
some cases, and there is no simple way to modify the code to suppress
the warning.

`-W'
     Print extra warning messages for these events:

        * A nonvolatile automatic variable might be changed by a call to
          `longjmp'.  These warnings as well are possible only in
          optimizing compilation.

          The compiler sees only the calls to `setjmp'.  It cannot know
          where `longjmp' will be called; in fact, a signal handler
          could call it at any point in the code.  As a result, you may
          get a warning even when there is in fact no problem because
          `longjmp' cannot in fact be called at the place which would
          cause a problem.

        * A function can return either with or without a value.
          (Falling off the end of the function body is considered
          returning without a value.)  For example, this function would
          evoke such a warning:

               foo (a)
               {
                 if (a > 0)
                   return a;
               }

        * An expression-statement or the left-hand side of a comma
          expression contains no side effects.  To suppress the
          warning, cast the unused expression to void.  For example, an
          expression such as `x[i,j]' will cause a warning, but
          `x[(void)i,j]' will not.

        * An unsigned value is compared against zero with `<' or `<='.

        * A comparison like `x<=y<=z' appears; this is equivalent to
          `(x<=y ? 1 : 0) <= z', which is a different interpretation
          from that of ordinary mathematical notation.

        * Storage-class specifiers like `static' are not the first
          things in a declaration.  According to the C Standard, this
          usage is obsolescent.

        * If `-Wall' or `-Wunused' is also specified, warn about unused
          arguments.

        * A comparison between signed and unsigned values could produce
          an incorrect result when the signed value is converted to
          unsigned.  (But don't warn if `-Wno-sign-compare' is also
          specified.)

        * An aggregate has a partly bracketed initializer.  For
          example, the following code would evoke such a warning,
          because braces are missing around the initializer for `x.h':

               struct s { int f, g; };
               struct t { struct s h; int i; };
               struct t x = { 1, 2, 3 };

        * An aggregate has an initializer which does not initialize all
          members.  For example, the following code would cause such a
          warning, because `x.h' would be implicitly initialized to
          zero:

               struct s { int f, g, h; };
               struct s x = { 3, 4 };

`-Wtraditional'
     Warn about certain constructs that behave differently in
     traditional and ANSI C.

        * Macro arguments occurring within string constants in the
          macro body.  These would substitute the argument in
          traditional C, but are part of the constant in ANSI C.

        * A function declared external in one block and then used after
          the end of the block.

        * A `switch' statement has an operand of type `long'.

`-Wundef'
     Warn if an undefined identifier is evaluated in an `#if' directive.

`-Wshadow'
     Warn whenever a local variable shadows another local variable.

`-Wid-clash-LEN'
     Warn whenever two distinct identifiers match in the first LEN
     characters.  This may help you prepare a program that will compile
     with certain obsolete, brain-damaged compilers.

`-Wlarger-than-LEN'
     Warn whenever an object of larger than LEN bytes is defined.

`-Wpointer-arith'
     Warn about anything that depends on the "size of" a function type
     or of `void'.  GNU C assigns these types a size of 1, for
     convenience in calculations with `void *' pointers and pointers to
     functions.

`-Wbad-function-cast'
     Warn whenever a function call is cast to a non-matching type.  For
     example, warn if `int malloc()' is cast to `anything *'.

`-Wcast-qual'
     Warn whenever a pointer is cast so as to remove a type qualifier
     from the target type.  For example, warn if a `const char *' is
     cast to an ordinary `char *'.

`-Wcast-align'
     Warn whenever a pointer is cast such that the required alignment
     of the target is increased.  For example, warn if a `char *' is
     cast to an `int *' on machines where integers can only be accessed
     at two- or four-byte boundaries.

`-Wwrite-strings'
     Give string constants the type `const char[LENGTH]' so that
     copying the address of one into a non-`const' `char *' pointer
     will get a warning.  These warnings will help you find at compile
     time code that can try to write into a string constant, but only
     if you have been very careful about using `const' in declarations
     and prototypes.  Otherwise, it will just be a nuisance; this is
     why we did not make `-Wall' request these warnings.

`-Wconversion'
     Warn if a prototype causes a type conversion that is different
     from what would happen to the same argument in the absence of a
     prototype.  This includes conversions of fixed point to floating
     and vice versa, and conversions changing the width or signedness
     of a fixed point argument except when the same as the default
     promotion.

     Also, warn if a negative integer constant expression is implicitly
     converted to an unsigned type.  For example, warn about the
     assignment `x = -1' if `x' is unsigned.  But do not warn about
     explicit casts like `(unsigned) -1'.

`-Wsign-compare'
     Warn when a comparison between signed and unsigned values could
     produce an incorrect result when the signed value is converted to
     unsigned.  This warning is also enabled by `-W'; to get the other
     warnings of `-W' without this warning, use `-W -Wno-sign-compare'.

`-Waggregate-return'
     Warn if any functions that return structures or unions are defined
     or called.  (In languages where you can return an array, this also
     elicits a warning.)

`-Wstrict-prototypes'
     Warn if a function is declared or defined without specifying the
     argument types.  (An old-style function definition is permitted
     without a warning if preceded by a declaration which specifies the
     argument types.)

`-Wmissing-prototypes'
     Warn if a global function is defined without a previous prototype
     declaration.  This warning is issued even if the definition itself
     provides a prototype.  The aim is to detect global functions that
     fail to be declared in header files.

`-Wmissing-declarations'
     Warn if a global function is defined without a previous
     declaration.  Do so even if the definition itself provides a
     prototype.  Use this option to detect global functions that are
     not declared in header files.

`-Wredundant-decls'
     Warn if anything is declared more than once in the same scope,
     even in cases where multiple declaration is valid and changes
     nothing.

`-Wnested-externs'
     Warn if an `extern' declaration is encountered within an function.

`-Winline'
     Warn if a function can not be inlined, and either it was declared
     as inline, or else the `-finline-functions' option was given.

`-Wold-style-cast'
     Warn if an old-style (C-style) cast is used within a program.

`-Woverloaded-virtual'
     Warn when a derived class function declaration may be an error in
     defining a virtual function (C++ only).  In a derived class, the
     definitions of virtual functions must match the type signature of a
     virtual function declared in the base class.  With this option, the
     compiler warns when you define a function with the same name as a
     virtual function, but with a type signature that does not match any
     declarations from the base class.

`-Wsynth (C++ only)'
     Warn when g++'s synthesis behavior does not match that of cfront.
     For instance:

          struct A {
            operator int ();
            A& operator = (int);
          };
          
          main ()
          {
            A a,b;
            a = b;
          }

     In this example, g++ will synthesize a default `A& operator =
     (const A&);', while cfront will use the user-defined `operator ='.

`-Wlong-long'
     Warn if `long long' type is used.  This is default.  To inhibit
     the warning messages, use `-Wno-long-long'.  Flags `-Wlong-long'
     and `-Wno-long-long' are taken into account only when `-pedantic'
     flag is used.

`-Werror'
     Make all warnings into errors.


File: gcc.info,  Node: Debugging Options,  Next: Optimize Options,  Prev: Warning Options,  Up: Invoking GCC

Options for Debugging Your Program or GNU CC
============================================

   GNU CC has various special options that are used for debugging
either your program or GCC:

`-g'
     Produce debugging information in the operating system's native
     format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
     debugging information.

     On most systems that use stabs format, `-g' enables use of extra
     debugging information that only GDB can use; this extra information
     makes debugging work better in GDB but will probably make other
     debuggers crash or refuse to read the program.  If you want to
     control for certain whether to generate the extra information, use
     `-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', `-gdwarf-1+', or
     `-gdwarf-1' (see below).

     Unlike most other C compilers, GNU CC allows you to use `-g' with
     `-O'.  The shortcuts taken by optimized code may occasionally
     produce surprising results: some variables you declared may not
     exist at all; flow of control may briefly move where you did not
     expect it; some statements may not be executed because they
     compute constant results or their values were already at hand;
     some statements may execute in different places because they were
     moved out of loops.

     Nevertheless it proves possible to debug optimized output.  This
     makes it reasonable to use the optimizer for programs that might
     have bugs.

     The following options are useful when GNU CC is generated with the
     capability for more than one debugging format.

`-ggdb'
     Produce debugging information for use by GDB.  This means to use
     the most expressive format available (DWARF 2, stabs, or the
     native format if neither of those are supported), including GDB
     extensions if at all possible.

`-gstabs'
     Produce debugging information in stabs format (if that is
     supported), without GDB extensions.  This is the format used by
     DBX on most BSD systems.  On MIPS, Alpha and System V Release 4
     systems this option produces stabs debugging output which is not
     understood by DBX or SDB.  On System V Release 4 systems this
     option requires the GNU assembler.

`-gstabs+'
     Produce debugging information in stabs format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gcoff'
     Produce debugging information in COFF format (if that is
     supported).  This is the format used by SDB on most System V
     systems prior to System V Release 4.

`-gxcoff'
     Produce debugging information in XCOFF format (if that is
     supported).  This is the format used by the DBX debugger on IBM
     RS/6000 systems.

`-gxcoff+'
     Produce debugging information in XCOFF format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program, and may cause
     assemblers other than the GNU assembler (GAS) to fail with an
     error.

`-gdwarf'
     Produce debugging information in DWARF version 1 format (if that is
     supported).  This is the format used by SDB on most System V
     Release 4 systems.

`-gdwarf+'
     Produce debugging information in DWARF version 1 format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gdwarf-2'
     Produce debugging information in DWARF version 2 format (if that is
     supported).  This is the format used by DBX on IRIX 6.

`-gLEVEL'
`-ggdbLEVEL'
`-gstabsLEVEL'
`-gcoffLEVEL'
`-gxcoffLEVEL'
`-gdwarfLEVEL'
`-gdwarf-2LEVEL'
     Request debugging information and also use LEVEL to specify how
     much information.  The default level is 2.

     Level 1 produces minimal information, enough for making backtraces
     in parts of the program that you don't plan to debug.  This
     includes descriptions of functions and external variables, but no
     information about local variables and no line numbers.

     Level 3 includes extra information, such as all the macro
     definitions present in the program.  Some debuggers support macro
     expansion when you use `-g3'.

`-p'
     Generate extra code to write profile information suitable for the
     analysis program `prof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-pg'
     Generate extra code to write profile information suitable for the
     analysis program `gprof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-a'
     Generate extra code to write profile information for basic blocks,
     which will record the number of times each basic block is
     executed, the basic block start address, and the function name
     containing the basic block.  If `-g' is used, the line number and
     filename of the start of the basic block will also be recorded.
     If not overridden by the machine description, the default action is
     to append to the text file `bb.out'.

     This data could be analyzed by a program like `tcov'.  Note,
     however, that the format of the data is not what `tcov' expects.
     Eventually GNU `gprof' should be extended to process this data.

`-Q'
     Makes the compiler print out each function name as it is compiled,
     and print some statistics about each pass when it finishes.

`-ax'
     Generate extra code to profile basic blocks.  Your executable will
     produce output that is a superset of that produced when `-a' is
     used.  Additional output is the source and target address of the
     basic blocks where a jump takes place, the number of times a jump
     is executed, and (optionally) the complete sequence of basic
     blocks being executed.  The output is appended to file `bb.out'.

     You can examine different profiling aspects without recompilation.
     Your executable will read a list of function names from file
     `bb.in'.  Profiling starts when a function on the list is entered
     and stops when that invocation is exited.  To exclude a function
     from profiling, prefix its name with `-'.  If a function name is
     not unique, you can disambiguate it by writing it in the form
     `/path/filename.d:functionname'.  Your executable will write the
     available paths and filenames in file `bb.out'.

     Several function names have a special meaning:
    `__bb_jumps__'
          Write source, target and frequency of jumps to file `bb.out'.

    `__bb_hidecall__'
          Exclude function calls from frequency count.

    `__bb_showret__'
          Include function returns in frequency count.

    `__bb_trace__'
          Write the sequence of basic blocks executed to file
          `bbtrace.gz'.  The file will be compressed using the program
          `gzip', which must exist in your `PATH'.  On systems without
          the `popen' function, the file will be named `bbtrace' and
          will not be compressed.  *Profiling for even a few seconds on
          these systems will produce a very large file.*  Note:
          `__bb_hidecall__' and `__bb_showret__' will not affect the
          sequence written to `bbtrace.gz'.

     Here's a short example using different profiling parameters in
     file `bb.in'.  Assume function `foo' consists of basic blocks 1
     and 2 and is called twice from block 3 of function `main'.  After
     the calls, block 3 transfers control to block 4 of `main'.

     With `__bb_trace__' and `main' contained in file `bb.in', the
     following sequence of blocks is written to file `bbtrace.gz': 0 3
     1 2 1 2 4.  The return from block 2 to block 3 is not shown,
     because the return is to a point inside the block and not to the
     top.  The block address 0 always indicates, that control is
     transferred to the trace from somewhere outside the observed
     functions.  With `-foo' added to `bb.in', the blocks of function
     `foo' are removed from the trace, so only 0 3 4 remains.

     With `__bb_jumps__' and `main' contained in file `bb.in', jump
     frequencies will be written to file `bb.out'.  The frequencies are
     obtained by constructing a trace of blocks and incrementing a
     counter for every neighbouring pair of blocks in the trace.  The
     trace 0 3 1 2 1 2 4 displays the following frequencies:

          Jump from block 0x0 to block 0x3 executed 1 time(s)
          Jump from block 0x3 to block 0x1 executed 1 time(s)
          Jump from block 0x1 to block 0x2 executed 2 time(s)
          Jump from block 0x2 to block 0x1 executed 1 time(s)
          Jump from block 0x2 to block 0x4 executed 1 time(s)

     With `__bb_hidecall__', control transfer due to call instructions
     is removed from the trace, that is the trace is cut into three
     parts: 0 3 4, 0 1 2 and 0 1 2.  With `__bb_showret__', control
     transfer due to return instructions is added to the trace.  The
     trace becomes: 0 3 1 2 3 1 2 3 4.  Note, that this trace is not
     the same, as the sequence written to `bbtrace.gz'.  It is solely
     used for counting jump frequencies.

`-fprofile-arcs'
     Instrument "arcs" during compilation.  For each function of your
     program, GNU CC creates a program flow graph, then finds a
     spanning tree for the graph.  Only arcs that are not on the
     spanning tree have to be instrumented: the compiler adds code to
     count the number of times that these arcs are executed.  When an
     arc is the only exit or only entrance to a block, the
     instrumentation code can be added to the block; otherwise, a new
     basic block must be created to hold the instrumentation code.

     Since not every arc in the program must be instrumented, programs
     compiled with this option run faster than programs compiled with
     `-a', which adds instrumentation code to every basic block in the
     program.  The tradeoff: since `gcov' does not have execution
     counts for all branches, it must start with the execution counts
     for the instrumented branches, and then iterate over the program
     flow graph until the entire graph has been solved.  Hence, `gcov'
     runs a little more slowly than a program which uses information
     from `-a'.

     `-fprofile-arcs' also makes it possible to estimate branch
     probabilities, and to calculate basic block execution counts.  In
     general, basic block execution counts do not give enough
     information to estimate all branch probabilities.  When the
     compiled program exits, it saves the arc execution counts to a
     file called `SOURCENAME.da'.  Use the compiler option
     `-fbranch-probabilities' (*note Options that Control Optimization:
     Optimize Options.) when recompiling, to optimize using estimated
     branch probabilities.

`-ftest-coverage'
     Create data files for the `gcov' code-coverage utility (*note
     `gcov': a GNU CC Test Coverage Program: Gcov.).  The data file
     names begin with the name of your source file:

    `SOURCENAME.bb'
          A mapping from basic blocks to line numbers, which `gcov'
          uses to associate basic block execution counts with line
          numbers.

    `SOURCENAME.bbg'
          A list of all arcs in the program flow graph.  This allows
          `gcov' to reconstruct the program flow graph, so that it can
          compute all basic block and arc execution counts from the
          information in the `SOURCENAME.da' file (this last file is
          the output from `-fprofile-arcs').

`-Q'
     Makes the compiler print out each function name as it is compiled,
     and print some statistics about each pass when it finishes.

`-dLETTERS'
     Says to make debugging dumps during compilation at times specified
     by LETTERS.  This is used for debugging the compiler.  The file
     names for most of the dumps are made by appending a word to the
     source file name (e.g.  `foo.c.rtl' or `foo.c.jump').  Here are the
     possible letters for use in LETTERS, and their meanings:

    `b'
          Dump after computing branch probabilities, to `FILE.bp'.

    `c'
          Dump after instruction combination, to the file
          `FILE.combine'.

    `d'
          Dump after delayed branch scheduling, to `FILE.dbr'.

    `D'
          Dump all macro definitions, at the end of preprocessing, in
          addition to normal output.

    `y'
          Dump debugging information during parsing, to standard error.

    `r'
          Dump after RTL generation, to `FILE.rtl'.

    `x'
          Just generate RTL for a function instead of compiling it.
          Usually used with `r'.

    `j'
          Dump after first jump optimization, to `FILE.jump'.

    `s'
          Dump after CSE (including the jump optimization that sometimes
          follows CSE), to `FILE.cse'.

    `F'
          Dump after purging ADDRESSOF, to `FILE.addressof'.

    `f'
          Dump after flow analysis, to `FILE.flow'.

    `g'
          Dump after global register allocation, to `FILE.greg'.

    `G'
          Dump after GCSE, to `FILE.gcse'.

    `j'
          Dump after first jump optimization, to `FILE.jump'.

    `J'
          Dump after last jump optimization, to `FILE.jump2'.

    `k'
          Dump after conversion from registers to stack, to
          `FILE.stack'.

    `l'
          Dump after local register allocation, to `FILE.lreg'.

    `L'
          Dump after loop optimization, to `FILE.loop'.

    `M'
          Dump after performing the machine dependent reorganisation
          pass, to `FILE.mach'.

    `N'
          Dump after the register move pass, to `FILE.regmove'.

    `r'
          Dump after RTL generation, to `FILE.rtl'.

    `R'
          Dump after the second instruction scheduling pass, to
          `FILE.sched2'.

    `s'
          Dump after CSE (including the jump optimization that
          sometimes follows CSE), to `FILE.cse'.

    `S'
          Dump after the first instruction scheduling pass, to
          `FILE.sched'.

    `t'
          Dump after the second CSE pass (including the jump
          optimization that sometimes follows CSE), to `FILE.cse2'.

    `x'
          Just generate RTL for a function instead of compiling it.
          Usually used with `r'.

    `a'
          Produce all the dumps listed above.

    `m'
          Print statistics on memory usage, at the end of the run, to
          standard error.

    `p'
          Annotate the assembler output with a comment indicating which
          pattern and alternative was used.

    `y'
          Dump debugging information during parsing, to standard error.

    `A'
          Annotate the assembler output with miscellaneous debugging
          information.

`-fpretend-float'
     When running a cross-compiler, pretend that the target machine
     uses the same floating point format as the host machine.  This
     causes incorrect output of the actual floating constants, but the
     actual instruction sequence will probably be the same as GNU CC
     would make when running on the target machine.

`-save-temps'
     Store the usual "temporary" intermediate files permanently; place
     them in the current directory and name them based on the source
     file.  Thus, compiling `foo.c' with `-c -save-temps' would produce
     files `foo.i' and `foo.s', as well as `foo.o'.

`-print-file-name=LIBRARY'
     Print the full absolute name of the library file LIBRARY that
     would be used when linking--and don't do anything else.  With this
     option, GNU CC does not compile or link anything; it just prints
     the file name.

`-print-prog-name=PROGRAM'
     Like `-print-file-name', but searches for a program such as `cpp'.

`-print-libgcc-file-name'
     Same as `-print-file-name=libgcc.a'.

     This is useful when you use `-nostdlib' or `-nodefaultlibs' but
     you do want to link with `libgcc.a'.  You can do

          gcc -nostdlib FILES... `gcc -print-libgcc-file-name`

`-print-search-dirs'
     Print the name of the configured installation directory and a list
     of program and library directories gcc will search--and don't do
     anything else.

     This is useful when gcc prints the error message `installation
     problem, cannot exec cpp: No such file or directory'.  To resolve
     this you either need to put `cpp' and the other compiler
     components where gcc expects to find them, or you can set the
     environment variable `GCC_EXEC_PREFIX' to the directory where you
     installed them.  Don't forget the trailing '/'.  *Note Environment
     Variables::.

