I would like to migrate from Qt 5.6 to Qt 5.7 on my workstation running centos 6.7. Everything's fine with Qt 5.6 but i am facing the following issue with Qt 5.7 after i have downloaded and installed it.
I am trying to run the elasticnode examples to check the installation but i have the following build error:
cc1plus: error: unrecognized command line option "-std=gnu++11"
This error is related to the version of gcc which is 4.4.7 and does not recognize this option. The compiler flag used by Qt 5.7 to activate c++11 features is -std=gnu++11 and with Qt 5.6 it was -std=gnu++0x and only this last flag is recognized by gcc.
In the .pro file of the elasticnodes example, nothing is set and so i assume that c+11 was disabled by default as described in the documentation http://doc.qt.io/qt-5/qmake-variable-reference.html#config but this is not consistent with the gcc command line that is finally generated by qmake.
So my question is , how to remove the new flag and set the old flag back in the .pro file , that is -std=gnu++0x instead of -std=gnu++11 ?
I have tried to add the following lines :
CONFIG -= c++11
QMAKE_CXXFLAGS += -std=gnu++0x
but i get this error :
/opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qbasicatomic.h:61: error: #error "Qt requires C++11 support"
Does anyone knows how to properly set this flag ?
Qt 5.7 requires a C++11 compiler. The minimum supported GCC version is therefore GCC 4.6 (but higher versions are highly recommended). You can install a devtoolset (say, devtoolset-2, see here) to get a better compiler.