|Using the GNU Compiler Collection (GCC)|
The GNU compiler provides these extensions to the C++ language (and you
can also use most of the C language extensions in your C++ programs). If you
want to write code that checks whether these features are available, you can
test for the GNU compiler the same way as for C programs: check for a
__GNUC__. You can also use
test specifically for GNU C++ (see Predefined Macros).