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

which operating system and compiler you are using and version of both? Check if the environment variables of the install is correct, for example Where is the headers of c++?. A variation is to add the path of the "includes of your headers" to the project configuration in the left panel go to "project - program - target" and add the path of the includes. another is to add the full path to the location of the c++ standard headers to the variable "includepath" in your .pro file.