What files could have been included?

Question

I would like to be able to get a list of all possible files included in a C source file.

I understand there are complications with other # directives (for instance, an #ifdef could either prevent an include or cause an extra include). All I'm looking for is a list of files that may have been included.

Is there a tool that already does this?

The files I'm compiling are only going to .o, and the standard C libraries are not included. I know that sounds wonky, but we have our reasons.

The reason I want to be able to do this is I want to have a list of files which may have contributed something to the .o, so I can check to see if they have changed.

Answer 1

Quoting the man page for gcc:

-M  Instead of outputting the result of preprocessing, output a rule
    suitable for make describing the dependencies of the main source
    file.  The preprocessor outputs one make rule containing the object
    file name for that source file, a colon, and the names of all the
    included files, including those coming from -include or -imacros
    command line options.

This basically does what you want. There are several other related options (all starting with -M) that give you different variants of this output.

Answer 2

my syntax is rusty, but ...

grep -ir "#include " *.c

might work ...