Configuring the GCC compiler switches in Qt, QtCreator, and QMake

It boils down to reading the manual. Instead of using CXXFLAGS in the .pro file, you need to use QMAKE_CXXFLAGS as in:

main.cpp:

#include <cinttypes>

int main() { return 0; }

main.pro:

SOURCES += main.cpp
QMAKE_CXXFLAGS += -std=c++0x