Re: [Predef-contribute] Meaning of __GNUC__

[Bjorn R. <br...@ma...>]

Ming Kin Lai wrote:

> Currently, in the Pre-defined Compiler Macros for Compilers web page, __GNUC__ is listed as an identification macro for GNU C/C++ compiler.  After some research and
> discussion with others, I believe it is not exactly accurate, though it used to be
> correct some years ago.
[...]
> 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.  Currently there is no macro
> to identify the compiler as the GNU C Compiler.

Ok, I have changed the note of caution to:

 "Please note that the meaning of the __GNUC__ macro has changed subtly
  over the years, from identifying the GNU C/C++ compiler to identifying
  any compiler that implements the GNU compiler extensions (see "Feature
  request - a macro defined for GCC" [1] discussion for further
  information). For example, the Intel C++ on Linux also defines these
  macros from version 8.1 (see the "Intel C++ Compiler 8.1 for Linux
  Release Notes" [2] and "Intel Compilers for Linux: Compatibility with
  GNU Compilers" [3].)"

where

[1] http://gcc.gnu.org/ml/gcc/2008-07/threads.html#00025
[2]
ftp://download.intel.com/support/performancetools/c/linux/sb/clin81_relnotes.pdf
[3] http://www.intel.com/cd/software/products/asmo-na/eng/284736.htm

Is this a satisfactory description?

> And look even more carefully at what the current CPP Manual says:
> "These macros are defined by all GNU compilers that use the C preprocessor: C, 
>  C++, Objective-C and Fortran".  That is, the GNU Fortran Compiler also has 
> __GNU__ defined.  Note that now GCC means GNU Compiler Collection, not GNU C 

I consider Objective-C and Fortran out of scope for the predef pages,
which only targets people writing C and C++ source code files.