#include directive: relative to where?

Question

I have looked in The C++ Programming Language to try to find the answer to this. When I #include "my_dir/my_header.hpp" in a header, where does it look for this file? Is it relative to the header, relative to the source file that included it, or something else?

Answer 1

Implementation defined. See what is the difference between #include <filename> and #include “filename”.