re PR c/28368 (-std=c89 doesn't warn about gcc's "?:" extension)

2008-02-16  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

	PR c/28368
	* doc/invoke.texi (-std): Clarify description of -std= and -ansi.

From-SVN: r132367

gcc/ChangeLog

+2008-02-16  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>
+
+	PR c/28368
+	* doc/invoke.texi (-std): Clarify description of -std= and -ansi.
+
 2008-02-16  Ralf Corsepius  <ralf.corsepius@rtems.org>
 
 	* config/m68k/t-rtems (M68K_MLIB_CPU): Add 5208, 5307, 5407, 5475

gcc/doc/invoke.texi

@@ -1335,12 +1335,31 @@ Determine the language standard. @xref{Standards,,Language Standards
 Supported by GCC}, for details of these standard versions.  This option
 is currently only supported when compiling C or C++. 
 
+The compiler can accept several base standards, such as @samp{c89} or
+@samp{c++98}, and GNU dialects of those standards, such as
+@samp{gnu89} or @samp{gnu++98}.  By specifing a base standard, the
+compiler will accept all programs following that standard and those
+using GNU extensions that do not contradict it.  For example,
+@samp{-std=c89} turns off certain features of GCC that are
+incompatible with ISO C90, such as the @code{asm} and @code{typeof}
+keywords, but not other GNU extensions that do not have a meaning in
+ISO C90, such as omitting the middle term of a @code{?:}
+expression. On the other hand, by specifing a GNU dialect of a
+standard, all features the compiler support are enabled, even when
+those features change the meaning of the base standard and some
+strict-conforming programs may be rejected.  The particular standard
+is used by @option{-pedantic} to identify which features are GNU
+extensions given that version of the standard. For example
+@samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
+comments, while @samp{-std=gnu99 -pedantic} would not.
+
 A value for this option must be provided; possible values are
 
 @table @samp
 @item c89
 @itemx iso9899:1990
-ISO C90 (same as @option{-ansi}).
+Support all ISO C90 programs (certain GNU extensions that conflict
+with ISO C90 are disabled). Same as @option{-ansi} for C code.
 
 @item iso9899:199409
 ISO C90 as modified in amendment 1.
@@ -1354,19 +1373,21 @@ ISO C99.  Note that this standard is not yet fully supported; see
 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
 
 @item gnu89
-Default, ISO C90 plus GNU extensions (including some C99 features).
+GNU dialect of ISO C90 (including some C99 features). This
+is the default for C code.
 
 @item gnu99
 @itemx gnu9x
-ISO C99 plus GNU extensions.  When ISO C99 is fully implemented in GCC,
+GNU dialect of ISO C99.  When ISO C99 is fully implemented in GCC,
 this will become the default.  The name @samp{gnu9x} is deprecated.
 
 @item c++98
-The 1998 ISO C++ standard plus amendments.
+The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
+C++ code.
 
 @item gnu++98
-The same as @option{-std=c++98} plus GNU extensions.  This is the
-default for C++ code.
+GNU dialect of @option{-std=c++98}.  This is the default for
+C++ code.
 
 @item c++0x
 The working draft of the upcoming ISO C++0x standard. This option
@@ -1376,21 +1397,10 @@ enabled by this flag may be removed from future versions of GCC if it is
 not part of the C++0x standard.
 
 @item gnu++0x
-The same as @option{-std=c++0x} plus GNU extensions. As with
-@option{-std=c++0x}, this option enables experimental features that may
-be removed in future versions of GCC.
+GNU dialect of @option{-std=c++0x}. This option enables
+experimental features that may be removed in future versions of GCC.
 @end table
 
-Even when this option is not specified, you can still use some of the
-features of newer standards in so far as they do not conflict with
-previous C standards.  For example, you may use @code{__restrict__} even
-when @option{-std=c99} is not specified.
-
-The @option{-std} options specifying some version of ISO C have the same
-effects as @option{-ansi}, except that features that were not in ISO C90
-but are in the specified version (for example, @samp{//} comments and
-the @code{inline} keyword in ISO C99) are not disabled.
-
 @item -fgnu89-inline
 @opindex fgnu89-inline
 The option @option{-fgnu89-inline} tells GCC to use the traditional