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	   cialization of a templatized function.  Because this non-conforming
	   behavior is no longer the default behavior for G++, -Wnon-tem-
	   plate-friend allows the compiler to check existing code for poten-
	   tial trouble spots, and is on by default.  This new compiler behav-
	   ior can be turned off with -Wno-non-template-friend which keeps the
	   conformant compiler code but disables the helpful warning.

       -Wold-style-cast (C++ only)
	   Warn if an old-style (C-style) cast to a non-void type is used
	   within a C++ program.  The new-style casts (static_cast, reinter-
	   pret_cast, and const_cast) are less vulnerable to unintended
	   effects, and much easier to grep for.

       -Woverloaded-virtual (C++ only)
	   Warn when a function declaration hides virtual functions from a
	   base class.	For example, in:

		   struct A {
		     virtual void f();
		   };

		   struct B: public A {
		     void f(int);
		   };

	   the "A" class version of "f" is hidden in "B", and code like this:

		   B* b;
		   b->f();

	   will fail to compile.

       -Wno-pmf-conversions (C++ only)
	   Disable the diagnostic for converting a bound pointer to member
	   function to a plain pointer.

       -Wsign-promo (C++ only)
	   Warn when overload resolution chooses a promotion from unsigned or
	   enumeral type to a signed type over a conversion to an unsigned
	   type of the same size.  Previous versions of G++ would try to pre-
	   serve unsignedness, but the standard mandates the current behavior.

       -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 =.

       Options Controlling Objective-C Dialect

       This section describes the command-line options that are only meaning-
       ful for Objective-C programs; but you can also use most of the GNU com-
       piler options regardless of what language your program is in.  For
       example, you might compile a file "some_class.m" like this:

	       gcc -g -fgnu-runtime -O -c some_class.m

       In this example, only -fgnu-runtime is an option meant only for Objec-
       tive-C programs; you can use the other options with any language sup-
       ported by GCC.

       Here is a list of options that are only for compiling Objective-C pro-
       grams:

       -fconstant-string-class=class-name
	   Use class-name as the name of the class to instantiate for each
	   literal string specified with the syntax "@"..."".  The default
	   class name is "NXConstantString".

       -fgnu-runtime
	   Generate object code compatible with the standard GNU Objective-C
	   runtime.  This is the default for most types of systems.

       -fnext-runtime
	   Generate output compatible with the NeXT runtime.  This is the
	   default for NeXT-based systems, including Darwin and Mac OS X.

       -gen-decls
	   Dump interface declarations for all classes seen in the source file
	   to a file named sourcename.decl.

       -Wno-protocol
	   Do not warn if methods required by a protocol are not implemented
	   in the class adopting it.

       -Wselector
	   Warn if a selector has multiple methods of different types defined.

       Options to Control Diagnostic Messages Formatting

       Traditionally, diagnostic messages have been formatted irrespective of
       the output device's aspect (e.g. its width, ...).  The options
       described below can be used to control the diagnostic messages format-
       ting algorithm, e.g. how many characters per line, how often source
       location information should be reported.	 Right now, only the C++ front
       end can honor these options.  However it is expected, in the near
       future, that the remaining front ends would be able to digest them cor-
       rectly.

       -fmessage-length=n
	   Try to format error messages so that they fit on lines of about n
	   characters.	The default is 72 characters for g++ and 0 for the
	   rest of the front ends supported by GCC.  If n is zero, then no
	   line-wrapping will be done; each error message will appear on a
	   single line.

       -fdiagnostics-show-location=once
	   Only meaningful in line-wrapping mode.  Instructs the diagnostic
	   messages reporter to emit once source location information; that
	   is, in case the message is too long to fit on a single physical
	   line and has to be wrapped, the source location won't be emitted
	   (as prefix) again, over and over, in subsequent continuation lines.
	   This is the default behavior.

       -fdiagnostics-show-location=every-line
	   Only meaningful in line-wrapping mode.  Instructs the diagnostic
	   messages reporter to emit the same source location information (as
	   prefix) for physical lines that result from the process of breaking
	   a message which is too long to fit on a single line.

       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.

       The following options control the amount and kinds of warnings produced
       by GCC; for further, language-specific options also refer to @ref{C++
       Dialect Options} and @ref{Objective-C Dialect Options}.

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

       -pedantic
	   Issue all the warnings demanded by strict ISO C and ISO C++; reject
	   all programs that use forbidden extensions, and some other programs
	   that do not follow ISO C and ISO C++.  For ISO C, follows the ver-
	   sion of the ISO C standard specified by any -std option used.

	   Valid ISO C and ISO C++ programs should compile properly with or
	   without this option (though a rare few will require -ansi or a -std
	   option specifying the required version of ISO C).  However, without
	   this option, certain GNU extensions and traditional C and C++ fea-
	   tures 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__".  How-
	   ever, only system header files should use these escape routes;
	   application programs should avoid them.

	   Some users try to use -pedantic to check programs for strict ISO C
	   conformance.	 They soon find that it does not do quite what they
	   want: it finds some non-ISO practices, but not all---only those for
	   which ISO C requires a diagnostic, and some others for which diag-
	   nostics have been added.

	   A feature to report any failure to conform to ISO C might be useful
	   in some instances, but would require considerable additional work
	   and would be quite different from -pedantic.	 We don't have plans
	   to support such a feature in the near future.

	   Where the standard specified with -std represents a GNU extended
	   dialect of C, such as gnu89 or gnu99, there is a corresponding base
	   standard, the version of ISO C on which the GNU extended dialect is
	   based.  Warnings from -pedantic are given where they are required
	   by the base standard.  (It would not make sense for such warnings
	   to be given only for features not in the specified GNU C dialect,
	   since by definition the GNU dialects of C include all features the
	   compiler supports with the given option, and there would be nothing
	   to warn about.)

       -pedantic-errors
	   Like -pedantic, except that errors are produced rather than warn-
	   ings.

       -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, and that the conversions specified in the format string
	   make sense.	This includes standard functions, and others specified
	   by format attributes, in the "printf", "scanf", "strftime" and
	   "strfmon" (an X/Open extension, not in the C standard) families.

	   The formats are checked against the format features supported by
	   GNU libc version 2.2.  These include all ISO C89 and C99 features,
	   as well as features from the Single Unix Specification and some BSD
	   and GNU extensions.	Other library implementations may not support
	   all these features; GCC does not support warning about features
	   that go beyond a particular library's limitations.  However, if
	   -pedantic is used with -Wformat, warnings will be given about for-
	   mat features not in the selected standard version (but not for
	   "strfmon" formats, since those are not in any version of the C
	   standard).

	   -Wformat is included in -Wall.  For more control over some aspects
	   of format checking, the options -Wno-format-y2k, -Wno-for-
	   mat-extra-args, -Wformat-nonliteral, -Wformat-security and -Wfor-
	   mat=2 are available, but are not included in -Wall.

       -Wno-format-y2k
	   If -Wformat is specified, do not warn about "strftime" formats
	   which may yield only a two-digit year.

       -Wno-format-extra-args
	   If -Wformat is specified, do not warn about excess arguments to a
	   "printf" or "scanf" format function.	 The C standard specifies that
	   such arguments are ignored.

	   Where the unused arguments lie between used arguments that are
	   specified with $ operand number specifications, normally warnings
	   are still given, since the implementation could not know what type
	   to pass to "va_arg" to skip the unused arguments.  However, in the
	   case of "scanf" formats, this option will suppress the warning if
	   the unused arguments are all pointers, since the Single Unix Speci-
	   fication says that such unused arguments are allowed.

       -Wformat-nonliteral
	   If -Wformat is specified, also warn if the format string is not a
	   string literal and so cannot be checked, unless the format function
	   takes its format arguments as a "va_list".

       -Wformat-security
	   If -Wformat is specified, also warn about uses of format functions
	   that represent possible security problems.  At present, this warns
	   about calls to "printf" and "scanf" functions where the format
	   string is not a string literal and there are no format arguments,
	   as in "printf (foo);".  This may be a security hole if the format
	   string came from untrusted input and contains %n.  (This is cur-
	   rently a subset of what -Wformat-nonliteral warns about, but in
	   future warnings may be added to -Wformat-security that are not
	   included in -Wformat-nonliteral.)

       -Wformat=2
	   Enable -Wformat plus format checks not included in -Wformat.	 Cur-
	   rently equivalent to -Wformat -Wformat-nonliteral -Wformat-secu-
	   rity.

       -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.

       -Wmissing-braces
	   Warn if an aggregate or union initializer is not fully bracketed.
	   In the following example, the initializer for a is not fully brack-
	   eted, but that for b is fully bracketed.

		   int a[2][2] = { 0, 1, 2, 3 };
		   int b[2][2] = { { 0, 1 }, { 2, 3 } };

       -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)