Solved 'CONFIG += c++17' does not take an effect in .pro file.

[Dmitriano]

I have

CONFIG += c++17

in my .pro file, but getting the following compiler errors:

error C4984: 'if constexpr' is a C++17 language extension
error C7525: inline variables require at least '/std:c++17'

My QT version 5.13
Compiler: MSVC 2017.

[J.Hilk]

hi @Dmitriano
take a look at this bug report
https://bugreports.qt.io/browse/QTBUG-67527

seems like c++1z is the way to go.

[Dmitriano]

Hi @J.Hilk !
I do not know exactly what 'c++1z' is, but it has the same effect, there are still the same compiler errors. (I deleted the build directory and did a clean build).

[J.Hilk]

@Dmitriano did you make a complete rebuild of your project, clean -> qmake -> make?

Changing the pro file will require a complete recreation

[Dmitriano]

@J.Hilk
yes I replaced

#CONFIG += c++17
CONFIG += c++1z

removed the build directory and rebuilt the project.

[J.Hilk]

@Dmitriano
well I#m out of ideas,

according to this reference
https://doc.qt.io/qt-5/qmake-variable-reference.html

it should work, if your compiler supports it.
I would assume, that MSVC2017 does indeed support c++17 😟

[aha_1980]

@Dmitriano please show your compiler output. Both c++1z and c++17 should work in Qt 5.12 upwards. For version < 5.12, you need to specify c++17.

[Dmitriano]

@J.Hilk @aha_1980
Something went wrong after switching from 5.12 to 5.13. Probably I selected a wrong configuration 'VS2017 Desktop 64bit'. If I select 'Desktop Qt 5.13 MSVS2017 64bit' the project compiles.