Qt Creator can't find headers (says: “No such file or directory”)

Question

How can I tell Qt Creator 2.4.1 (based on Qt 4.7.4 32-bit) where to look by default for header files?

When I open a C file in Qt Creator and say

Answer 1

Standalone C++ files can be edited, but it is likely you will loose the functionality of #include's and autocomplete, among other thigns. I personally keep all my projects in Qt somehow, whether it is a simple GUI program that does one task, so I can debug it (gdb doesn't seem to like command line programs, atleast in my experience) or use a "Simple C++ command line" project for non-Qt dependent projects.