GCC dump preprocessor defines

gcc g++ c-preprocessor
Anycorn picture Anycorn · Feb 8, 2010 · Viewed 129k times · Source

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

Answer

philant picture philant · Feb 8, 2010

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

 gcc -dM -E - < /dev/null

For C++

 g++ -dM -E -x c++ - < /dev/null

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.

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