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Asked: 2026-05-30T17:46:37+00:00

Is there a way to list all C preprocessor defines? I’m on a mac

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Is there a way to list all C preprocessor defines?

I’m on a mac with a compiled from source gcc and

#if defined __APPLE__
#error "Apple"
#else
#error "Ahh"
#endif

is giving me:

error: #error "Ahh"

my compile configure options are:

${PWD}/../gcc/configure --prefix="${PWD}/../build/" --exec-prefix="${PWD}/../build/" --datadir="${PWD}/../build/" --target=avr --enable-languages=c --disable-libssp --disable-lto --disable-nls --disable-libgomp --disable-gdbtk --disable-threads --enable-poison-system-directories
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1 Answer

  1. Editorial Team

    If you are using gnu cpp, you can pass the option -dM to emit all defined macros. That is:

    $ cpp -dM foo.c

    will tell you everything that is defined for foo.c. There will be extra defines passed on the command line by make, and probably more things in config.h, but if you grab the output of make and rerun the commands with -Xpreprocessor -dM added you should see everything.

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