Where does gcc look for C and C++ header files?

Question

On a Unix system, where does gcc look for header files?

I spent a little time this morning looking for some system header files, so I thought this would be good info

Answer 1

You can create a file that attempts to include a bogus system header. If you run gcc in verbose mode on such a source, it will list all the system include locations as it looks for the bogus header.

$ echo "#include " > t.c; gcc -v t.c; rm t.c

[..]

#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i686-apple-darwin9/4.0.1/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.

[..]

t.c:1:32: error: bogus.h: No such file or directory