gcc defines different macors for .cxx and .cpp

[Ralf Fassel]

gcc 2.95.2 and 2.7.2.1 on IRIX 5
gcc 2.95.1 on IRIX 6

The manual states:

       For any given input file, the file name suffix determines what kind
    of compilation is done:
--<snip-snip>--
    `FILE.cc'
    `FILE.cxx'
    `FILE.cpp'
    `FILE.C'
	 C++ source code which must be preprocessed.  Note that in `.cxx',
	 the last two letters must both be literally `x'.  Likewise, `.C'
	 refers to a literal capital C.

But the predefined macros are different for .cpp and .cxx files on the
above systems if applied on an empty file:

% rm foo.cxx foo.cpp
% touch foo.cpp foo.cxx
% gcc -E -dM foo.cxx > cxx
% gcc -E -dM foo.cpp > cpp
% diff -c cxx cpp
*** cxx	Thu Apr 13 18:40:02 2000
--- cpp	Thu Apr 13 18:39:57 2000
***************
*** 1,9 ****
! #define _LANGUAGE_C_PLUS_PLUS 1 
! #define __LANGUAGE_C_PLUS_PLUS 1 
  #define __host_mips 1 
  #define __mips64 1 
  #define SYSTYPE_SVR4 1 
  #define __MIPSEB 1 
  #define __DSO__ 1 
  #define _MIPS_SZLONG 32 
  #define __EXCEPTIONS 1 
--- 1,9 ----
! #define __LANGUAGE_C 1 
  #define __host_mips 1 
  #define __mips64 1 
  #define SYSTYPE_SVR4 1 
  #define __MIPSEB 1 
+ #define _LANGUAGE_C 1 
  #define __DSO__ 1 
  #define _MIPS_SZLONG 32 
  #define __EXCEPTIONS 1 
***************
*** 37,42 ****
--- 37,43 ----
  #define __GNUG__ 2 
  #define __EXTENSIONS__ 1 
  #define _MIPS_ISA _MIPS_ISA_MIPS3 
+ #define LANGUAGE_C 1 
  #define __sgi__ 1 
  #define _COMPILER_VERSION 601 
  #define _MIPS_SIM _ABIN32 

As you can see from the diff output, .cxx files (and .cc and .C for
that matter) #define LANGUAGE_CPLUS_PLUS (and _cplusplus, not shown in
the diff), but .cpp files #define LANGUAGE_C (*and* _cplusplus).

If one uses the -v flag to gcc, it is obvious that the difference
comes from the calling of the preprocessor:

% gcc -E -dM -v foo.cxx > /dev/null
gcc version 2.7.2.1
 /software/gcc/2.7.2.1/IRIX-5/lib/gcc-lib/mips-sgi-irix5.3/2.7.2.1/cpp
 -lang-c++ -v -undef -D__GNUC__=2 -D__GNUG__=2 -D__cplusplus
--<snip-snip>--
 -D_LONGLONG -D_LANGUAGE_C_PLUS_PLUS -D_MIPS_FPSET=16
             ^^^^^^^^^^^^^^^^^^^^^^^

% gcc -E -dM -v foo.cpp > /dev/null
gcc version 2.7.2.1
 /software/gcc/2.7.2.1/IRIX-5/lib/gcc-lib/mips-sgi-irix5.3/2.7.2.1/cpp
 -lang-c++ -v -undef -D__GNUC__=2 -D__GNUG__=2 -D__cplusplus
--<snip-snip>--
 -D_LONGLONG -D_LANGUAGE_C -DLANGUAGE_C -D_MIPS_FPSET=16
             ^^^^^^^^^^^^^^^^^^^^^^^^^^

Is this intentional?  From the sources in gcc.c, `.cpp' and `.cxx'
both are linked to {"#C++"}, so it looks like a bug or a compilation
problem to me.

This does not happen in gcc 2.7.2.1 on SunOS 5 or HP-UX-9 (neither
*LANGUAGE* macros is deifned there).

Please CC any response to me, since I'm not on the mailing list.
Thanks for listening.

R'