Determining where header file is found

Question

When I compile with gcc -v hello.c^*, the output shows a search path for #include:

$ gcc -v hello.c
Apple LLVM version 9.1.0 (clang-902.0.39.2)
Target: x86_64-apple-darwin17.7.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
...
clang -cc1 version 9.1.0 (clang-902.0.39.2) default target x86_64-apple-darwin17.7.0
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Library/Developer/CommandLineTools/usr/lib/clang/9.1.0/include
 /Library/Developer/CommandLineTools/usr/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.

Is there a way to determine definitively which of these locations is used? For example, say that hello.c contained #include <stdio.h>. I can see manually that there are versions of stdio.h in multiple locations, presumably which can use different function construction:

$ find /usr/local/include -name "stdio.h"
/usr/local/include/c++/5.5.0/tr1/stdio.h

$ find /Library/Developer/CommandLineTools/usr/include -name "stdio.h"
/Library/Developer/CommandLineTools/usr/include/c++/v1/stdio.h

$ find /usr/include -name "stdio.h"
/usr/include/c++/4.2.1/tr1/stdio.h
/usr/include/sys/stdio.h
/usr/include/stdio.h

In Python, this would look something like:

>>> import math
>>> math.__file__
'/Users/brad/miniconda3/lib/python3.6/lib-dynload/math.cpython-36m-darwin.so'

---

_{*I'm on a Macbook, so gcc actually seems to route to clang, although it appears to be a bona fide executable rather than symlink.}

Answer 1

From gcc man page:

-H

Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the #include stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid precompiled header file is printed with ...x and a valid one with ...! .