How can I get a list of all preprocessor symbols used (or defined) within a file?

Question

I have a number of C/C++ project files. I'd like to know the full list of preprocessor symbols used by the files. Is there a flag to gcc, or is there some tool I can use to get this list.

Optionally, if the tool also told me the list of symbols defined by the file, that would be great.

Answer 1

Use gcc -E -dM <file_list> - preprocess, then output #defines.

My gcc is a tad rusty, so I'm not sure whether or not you explicitly need the -E, but try both?

For further reference, see this