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gccg++c-preprocessor

GCC dump preprocessor defines

Is there a way for gcc/g++ to dump its default preprocessor defines from the command line? I mean things like __GNUC__, __STDC__, and so on.

Solution

  • Yes, use -E -dM options instead of -c. Example (outputs them to standard output):

     echo | gcc -dM -E -
 echo | clang -dM -E -

    For C++

     echo | g++ -dM -E -x c++ -
 echo | clang++ -dM -E -x c++ -

    From the GCC manual:

    Instead of the normal output, generate a list of `#define' directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a way of finding out what is predefined in your version of the preprocessor. Assuming you have no file foo.h, the command

    touch foo.h; cpp -dM foo.h

    will show all the predefined macros.

    If you use -dM without the -E option, -dM is interpreted as a synonym for -fdump-rtl-mach.