Build errors with Qt 5.7 and clang (needs C++11)

[spinnau@…]

Qt >= 5.7.0 will require a C++11 compliant compiler to build.

On archlinux with gcc-6.1.1 and qt-5.7.0 OpenModelica master branch builds and runs fine without any changes.

Using clang-3.8.0 and qt-5.7.0 gives build errors like this from OMShellGUI:

In file included from commandcompletion.cpp:49:
In file included from /usr/include/qt/QtCore/QFile:1:
In file included from /usr/include/qt/QtCore/qfile.h:44:
In file included from /usr/include/qt/QtCore/qfiledevice.h:43:
In file included from /usr/include/qt/QtCore/qiodevice.h:43:
In file included from /usr/include/qt/QtCore/qglobal.h:1145:
In file included from /usr/include/qt/QtCore/qatomic.h:46:
/usr/include/qt/QtCore/qbasicatomic.h:61:4: error: "Qt requires C++11 support"

Simply adding -std=c++11 to the CXXFLAGS doesn't help, as in the qmake config files like ​OMEdit.config.in the CFLAGS and CPPFLAGS will be propagated to QMAKE_CXXFLAGS.

It's also not possible to add -std=c++11 to CFLAGS, as clang then raises an error at configure:

configure:2143: checking whether the C compiler works
configure:2165: clang -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -std=c++11 -D_FORTIFY_SOURCE=2 -DH5_USE_18_API -Wl,-O1,--sort-common,--as-needed,-z,relro conftest.c  >&5
error: invalid argument '-std=c++11' not allowed with 'C/ObjC'

I got it to work by adding the following changes to the qmake config files in my PKGBUILD before configure:

export CXXFLAGS="$CXXFLAGS -std=c++11"    
sed -i 's/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@$/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@ @CXXFLAGS@/' ./OMEdit/OMEdit/OMEditGUI/OMEdit.config.in
sed -i 's/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@$/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@ @CXXFLAGS@/' ./OMNotebook/OMNotebook/OMNotebookGUI/OMNotebook.config.in  
sed -i 's/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@$/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@ @CXXFLAGS@/' ./OMShell/OMShell/OMShellGUI/OMShell.config.in
sed -i 's/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@$/QMAKE_CXXFLAGS = @CFLAGS@ @CPPFLAGS@ @CXXFLAGS@/' ./OMPlot/OMPlot/OMPlotGUI/OMPlotGUI.config.in
sed -i 's/#QMAKE_CXXFLAGS   \*= -std=c++11$/QMAKE_CXXFLAGS   *= -std=c++11/' ./OMPlot/qwt/qwtbuild.pri

[spinnau@…]

The problem is fixed for OMEdit and OMPlot (including qwt) by the commits ​19a274 and ​f907e8, respectively.

The C++11 compiler flag should also be added to QMAKE_CXXFLAGS for OMNotebook and OMShell to close this issue.

[spinnau@…]

Fixed in ​87a6e8b/OMNotebook and ​3464745/OMShell.