How to tell where a header file is included from?

How can I tell where g++ was able to find an include file? Basically if I

#include <foo.h>

g++ will scan the search path, using any include options to add or alter the path. But, at the end of days, is there a way I can tell the absolute path of foo.h that g++ chose to compile? Especially relevant if there is more than one foo.h in the myriad of search paths.

Short of a way of accomplishing that... is there a way to get g++ to tell me what its final search path 开发者_开发知识库is after including defaults and all include options?

g++ -H ...

will also print the full path of include files in a format which shows which header includes which

This will give make dependencies which list absolute paths of include files:

gcc  -M showtime.c

If you don't want the system includes (i.e. #include <something.h>) then use:

gcc  -MM showtime.c

Sure use

g++ -E -dI  ... (whatever the original command arguments were)

If your build process is very complicated...

constexpr static auto iWillBreak = 
#include "where/the/heck/is/this/file.h"

This will (almost certainly) cause a compilation error near the top of the file in question. That should show you a compiler error with the path the compiler sees.

Obviously this is worse than the other answers, but sometimes this kind of hack is useful.

If you use -MM or one of the related options (-M, etc), you get just the list of headers that are included without having all the other preprocessor output (which you seem to get with the suggested g++ -E -dI solution).

For MSVC you can use the /showInclude option, which will display the files that are included.

(This was stated in a comment of Michael Burr on this answer but I wanted to make it more visible and therefore added it as a separate answer.)

Usability note: The compiler will emit this information to the standard error output which seems to be suppressed by default when using the windows command prompt. Use 2>&1 to redirect stderr to stdout to see it nonetheless.