Re: [boost] [predef] Status and review results?

Subject: Re: [boost] [predef] Status and review results?
From: Bjorn Reese (breese_at_[hidden])
Date: 2013-05-03 07:10:27

On 05/03/2013 06:40 AM, Rene Rivera wrote:

>> It also incorrectly says that it is GCC compiler. This is because Intel
>> likes to do that for compatibility with GCC (I believe clang also defines
>> __GNUC_).
>>
>
> This is actually intentional, even if a bit confusing. If a compiler
> decides that it wants to emulate another compiler it's OK for me to detect
> both compilers at once. It's then up to users to decide if the compiler
> does actually emulate the compiler correctly. Basically I err on the side
> of more information.

The following is a quote from the predef.sourceforge.net pages:

  "Notice 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 the "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].)"

[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://software.intel.com/en-us/articles/intel-compilers-for-linux-compatibility-with-gnu-compilers

The way to avoid false positives, is to know which other compilers
define the GCC macros, and test for these first. For instance:

#if defined(__INTEL_COMPILER)
// Do Intel stuff
#else
# if defined(__GNUC__)
// Do GCC stuff
# endif
#endif