> In any case, the documentation has in some sense misled you. __GNUC__ > is indeed defined by the compiler proper, not by the preprocessor. > But that in turn does not matter, as if any non-gcc compiler *did* use > the gcc preprocessor, it would do so via gcc -E.
> Googling "Intel C++ __GNUC__" shows several major projects have been > affected by this icc misfeature. Upon further checking the GNU CPP Manual, some interesting things are revealed. The current manual (http://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html#Common-Predefined-Macros) (version unspecified) says: __GNUC__ __GNUC_MINOR__ __GNUC_PATCHLEVEL__ These macros are defined by all GNU compilers that use the C preprocessor: C, C++, Objective-C and Fortran. ... These macros are also defined if you invoke the preprocessor directly. ... If all you need to know is whether or not your program is being compiled by GCC, or a non-GCC compiler that claims to accept the GNU C dialects, you can simply test __GNUC__. Therefore, Intel C++ Compiler's definition of __GNUC__ appears to be legitimate if Intel honestly makes a reasonable claim that its compiler accepts the GNU C dialects. In comparison, the GNU CPP 2.8.1 (1997) Manual (http://sunsite.ualberta.ca/Documentation/Gnu/gcc-2.8.1/html_node/cpp_13.html#SEC14) says: __GNUC__ This macro is defined if and only if this is GNU C. This macro is defined only when the entire GNU C compiler is in use; if you invoke the preprocessor directly, `__GNUC__' is undefined. It seems this 1997 definition is more strict: a non-GCC compiler should never define __GNUC__. In other words, in 1997, __GNUC__ can be used to uniquely identify the GNU C compiler, now it can't; and nothing can. On the other hand, the 1997 sentence "if you invoke the preprocessor directly, `__GNUC__' is undefined" is now replaced by "These macros are also defined if you invoke the preprocessor directly." I have not had the time to find out what "invoke the preprocessor directly" means ('gcc -E' ?) but now the implication is that a non-'GNU C'-compliant compiler that uses GNU CPP as its preprocessor would have __GNUC__ defined, unless it takes the extra effort to somehow undefine it. And this also raises an interesting question: "These macros are also defined if you invoke the preprocessor directly" seems to imply that __GNUC__ is defined by the preprocessor, not the compiler proper. This appears to contradict the claim in a previous post (see above quote) that "__GNUC__ is indeed defined by the compiler proper, not by the preprocessor." _________________________________________________________________ It’s a talkathon – but it’s not just talk. http://www.imtalkathon.com/?source=EML_WLH_Talkathon_JustTalk
