Disable the compiler optimiser for qmake examples

[pento]

qmake defaults to adding -O2 when compiling, which can cause gcov to miss that some lines were optimised out.

I fixed this by adding this setting to my .pro file:

QMAKE_CXXFLAGS_RELEASE -= -O2

[richelbilderbeek]

Thanks for sharing, this is great. I'll try to gradually ad this to my projects. Also your Pull Requests are welcomed :-)