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

You could do the preprocessor step only. Most compilers allow this.

Of course that would require some busywork reading the resulting file.

Answer 2

All POSSIBLE files? No way to do that.

Answer 3

my syntax is rusty, but ...

grep -ir "#include " *.c

might work ...

Answer 4

If you use gcc you can inspect preprocessor dump:

[~]> gcc -E /usr/include/cups/dir.h|grep "#"
# 1 "/usr/include/cups/dir.h"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "/usr/include/cups/dir.h"
# 26 "/usr/include/cups/dir.h"
# 1 "/usr/include/sys/stat.h" 1 3 4
# 73 "/usr/include/sys/stat.h" 3 4
# 1 "/usr/include/sys/_types.h" 1 3 4
# 32 "/usr/include/sys/_types.h" 3 4
# 1 "/usr/include/sys/cdefs.h" 1 3 4
# 33 "/usr/include/sys/_types.h" 2 3 4
# 1 "/usr/include/machine/_types.h" 1 3 4
# 34 "/usr/include/machine/_types.h" 3 4
# 1 "/usr/include/i386/_types.h" 1 3 4
# 37 "/usr/include/i386/_types.h" 3 4
# 70 "/usr/include/i386/_types.h" 3 4
# 35 "/usr/include/machine/_types.h" 2 3 4
# 34 "/usr/include/sys/_types.h" 2 3 4
# 58 "/usr/include/sys/_types.h" 3 4
# 94 "/usr/include/sys/_types.h" 3 4
# 74 "/usr/include/sys/stat.h" 2 3 4
# 1 "/usr/include/sys/_structs.h" 1 3 4
# 88 "/usr/include/sys/_structs.h" 3 4
# 79 "/usr/include/sys/stat.h" 2 3 4
# 152 "/usr/include/sys/stat.h" 3 4
# 228 "/usr/include/sys/stat.h" 3 4
# 248 "/usr/include/sys/stat.h" 3 4
# 422 "/usr/include/sys/stat.h" 3 4
# 27 "/usr/include/cups/dir.h" 2
# 42 "/usr/include/cups/dir.h"

Answer 5

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 6

Alas, simply grepping the source for #include is not guaranteed to be enough, because someone may have committed ...

#define tricksy(foo,bar) <foo##bar>
#define precious tricksy(ios, tream)
#include precious
int main(int, char **)
{
        std::cout << "Hobbits!" << std::endl;
        return 0;
}

... though you would be able to tell by inspection that something nonstandard was going on with the #include precious because of the missing <> or "".

A non-perverse example would be token-pasting different library root directories depending on command-line definitions.