Detect gcc as opposed to msvc / clang with macro

Question

I am working on a project that has been built with both gcc and msvc so far. We recently started building with clang as well.

There are some parts in the code, where platform-specific things are done:

#ifndef _WIN32 // ignore this in msvc #endif 

Since gcc has previously been the only non-windows build, this was equivalent to saying "do this only for gcc". But now it means "do this only for gcc and clang".

However there are still situations, where I would like to handle something specifically for gcc, and not for clang. Is there a simple and robust way to detect gcc, i.e.

#ifdef ??? // do this *only* for gcc #endif 

Answer 1

__GNUC__ __GNUC_MINOR__ __GNUC_PATCHLEVEL__ 

These macros are defined by all GNU compilers that use the C preprocessor: C, C++, Objective-C and Fortran. Their values are the major version, minor version, and patch level of the compiler, as integer constants. For example, GCC 3.2.1 will define __GNUC__ to 3, __GNUC_MINOR__ to 2, and __GNUC_PATCHLEVEL__ to 1. These macros are also defined if you invoke the preprocessor directly.

Also:

__GNUG__ 

The GNU C++ compiler defines this. Testing it is equivalent to testing (__GNUC__ && __cplusplus).

Source

Apparently, clang uses them too. However it also defines:

__clang__ __clang_major__ __clang_minor__ __clang_patchlevel__ 

So you can do:

#ifdef __GNUC__     #ifndef __clang__ ... 

Or even better (note the order):

#if defined(__clang__) .... #elif defined(__GNUC__) || defined(__GNUG__) .... #elif defined(_MSC_VER) ....