How can I use C++14 features when building qmake projects?

Question

I'm currently using C++11 features in my Qt applications. However, I'd like to use some of the new C++14 features in my applications.

To enable C++11 in a Qt application, one only needs to add one line in the qmake project file, namely:

CONFIG += c++11

or this for earlier versions:

QMAKE_CXXFLAGS += -std=c++1y

I already tried to do the same with C++14, but it didn't work. I changed the above mentioned line of the qmake project like this:

CONFIG += c++14

or this for earlier versions:

QMAKE_CXXFLAGS += -std=c++1y

After that, lots of compilation errors, that did not exist before, appear when trying to build the project. The project compiles fine, however, if I try to use any C++14 features, I get a compilation error. This is an example:

template<typename T>
constexpr T pi = T(3.1415926535897932385);

This is the corresponding error:

main.cpp:7: error: template declaration of 'constexpr const T pi'
constexpr T pi = T(3.1415926535897932385);  
          ^

How to enable C++14 features when using a qmake project in QtCreator?

I am using Qt 5.3.2, Qt Creator 3.2.1, and MinGW 4.8.2 32 bit.

Answer 1

This is now supported properly from Qt 5.4. You just type this into your qmake project file:

CONFIG += c++14

The necessary code change went in the middle of 2014 by Thiago:

Add support for CONFIG += c++14

I have just created the necessary documentation change:

Mention the c++14 CONFIG option in the qmake variable reference

Please note that variable templates are only supported from gcc 5.0, but then your code works just fine. This can be used for testing C++14 with older gcc:

main.cpp

#include <iostream>

int main()
{
    // Binary literals: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3472.pdf
    // Single-quotation-mark as a digit separator: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3781.pdf
    std::cout << 0b0001'0000'0001;
    return 0;
}

main.pro

TEMPLATE = app
TARGET = main
CONFIG -= qt
CONFIG += c++14
SOURCES += main.cpp

Build and Run

qmake && make && ./main

Output

257