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

Question

I recently tried to use Qt Creator 1.3.2, Qt 4.6.2, and GCC 4.4.0 (32-bit version) on Windows 7 (64-bit) to compile an application using some of the experimental C++0x extensions and encountered the following (fatal) error:

This file requires compiler and library support for the upcoming ISO C++ standard, C++0x. This support is currently experimental, and must be enabled with the -std=c++0x or -std=gnu++0x compiler options.

In my search for a solution, I came across the thread qmake and compiler flags?, and added the following to the .pro file:

CXXFLAGS += -std=c++0x

but that didn't seem to make a difference.

So, I expect there's some tag I need to add to the .pro (project) file, but I've never messed with the GCC compiler switches in Qt, QMake, and QtCreator before, and I am uncertain about the proper invokation / incantation. So, my question is how do you set GCC compiler switches when using QtCreator, QMake, and Qt?

Answer 1

When supported by Qt, the proper way is to do something like CONFIG += c++11 Then watch your compile window output, to see if the proper flag is added.

If Qt doesn't support this version of the standard, you have to pass the appropriate flag directly to the compiler, as andand said with QMAKE_CXXFLAGS += -std=c++0x

If both methods work, use the one with CONFIG, as this method let Qt choose the appropriate flags, based on which compiler you've selected, so it makes your code more portable. It also helps Qt Creator for code highlighting.

Answer 2

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

Answer 3

The only way that really works for me is to add it to QMAKE_CXXFLAGS.

The CONFIG += c++11 does not add -std=c++11 to the compile command.

Answer 4

You should use

CONFIG += c++11

to enable C++11 compiler flags automatically.

Look for .prf files in your qt installation. I don't know where they might be on windows, but on my Linux installation they are under /opt/Qt/5.4/gcc_64/mkspecs/features.

You might want to read the qmake documentation for that:

qmake can be set up with extra configuration features that are specified in feature (.prf) files. These extra features often provide support for custom tools that are used during the build process. To add a feature to the build process, append the feature name (the stem of the feature filename) to the CONFIG variable.

You can add your own features.

Here is what I found on my system. CONFIG += name will enable the feature:

./android/android_deployment_settings.prf
./android/android.prf
./build_pass.prf
./c++11.prf
./c++14.prf
./cmake_functions.prf
./configure.prf
./create_cmake.prf
./ctest_testcase_common.prf
./ctest_testcase_installed.prf
./ctest_testcase.prf
./dbusadaptors.prf
./dbusinterfaces.prf
./declarative_debug.prf
./default_post.prf
./default_pre.prf
./designer_defines.prf
./device_config.prf
./egl.prf
./exceptions_off.prf
./exceptions.prf
./exclusive_builds_post.prf
./exclusive_builds.prf
./gcov.prf
./include_source_dir.prf
./incredibuild_xge.prf
./java.prf
./lex.prf
./link_ltcg.prf
./link_pkgconfig.prf
./ltcg.prf
./mac/default_post.prf
./mac/default_pre.prf
./mac/objective_c.prf
./mac/rez.prf
./mac/sdk.prf
./moc.prf
./no_debug_info.prf
./precompile_header.prf
./qfeatures.prf
./qlalr.prf
./qml1_module.prf
./qml1_plugin.prf
./qml_debug.prf
./qml_module.prf
./qml_plugin.prf
./qmltestcase.prf
./qpa/basicunixfontdatabase.prf
./qpa/genericunixfontdatabase.prf
./qt_android_deps.prf
./qt_app.prf
./qt_build_config.prf
./qt_build_paths.prf
./qt_common.prf
./qt_config.prf
./qt_docs.prf
./qt_docs_targets.prf
./qt_example_installs.prf
./qt_functions.prf
./qt_headersclean.prf
./qt_helper_lib.prf
./qt_installs.prf
./qt_module_headers.prf
./qt_module.prf
./qt_module_pris.prf
./qt_parts.prf
./qt_plugin.prf
./qt.prf
./qt_targets.prf
./qt_tool.prf
./resolve_config.prf
./resolve_target.prf
./resources.prf
./silent.prf
./simd.prf
./spec_post.prf
./spec_pre.prf
./testcase.prf
./testcase_targets.prf
./testcocoon.prf
./testlib_defines.prf
./uic.prf
./unix/bsymbolic_functions.prf
./unix/dylib.prf
./unix/hide_symbols.prf
./unix/largefile.prf
./unix/opengl.prf
./unix/openvg.prf
./unix/separate_debug_info.prf
./unix/thread.prf
./unix/x11inc.prf
./unix/x11lib.prf
./unix/x11.prf
./unix/x11sm.prf
./use_c_linker.prf
./vxworks.prf
./warn_off.prf
./warn_on.prf
./wayland-scanner.prf
./win32/console.prf
./win32/default_pre.prf
./win32/dumpcpp.prf
./win32/idcidl.prf
./win32/msvc_mp.prf
./win32/opengl.prf
./win32/openvg.prf
./win32/qt_config.prf
./win32/qt_dll.prf
./win32/rtti_off.prf
./win32/rtti.prf
./win32/stl_off.prf
./win32/stl.prf
./win32/windeployqt.prf
./win32/windows.prf
./winrt/console.prf
./winrt/font_deployment.prf
./winrt/package_manifest.prf
./yacc.prf