Building Qt 5.15.2, -c++std c++14 actives C++17 support

mblanchard

Hello,
I'm trying to build Qt 5.15.2 on CentOS 7 + GCC 8.3.1 without C++17 but C++14 support. Running something like:

./configure -opensource -confirm-license -release -shared -R \$ORIGIN -c++std c++14 ...

Ends-up generating build configuration like:

Configure summary:

Build type: linux-g++ (x86_64, CPU features: mmx sse sse2)
Compiler: gcc 8.3.1
Configuration: sse2 aesni compile_examples enable_new_dtags largefile precompile_header rdrnd shani sse3 ssse3 sse4_1 sse4_2 x86SimdAlways shared shared rpath release c++11 c++14 c++17 concurrent dbus reduce_exports reduce_relocations stl
Build options:
  Mode ................................... release
  Optimize release build for size ........ no
  Building shared libraries .............. yes
  Using C standard ....................... C11
  Using C++ standard ..................... C++17
...

Indeed, GCC 8 supports C++17 but I need a C++14 build and it seems like the -c++std c++14 flag does not restrict le standard level here...
Any idea how I can get Qt's build system to enforce a C++ standard level ?
Thanks!

Christian Ehrlicher

@mblanchard said in Building Qt 5.15.2, -c++std c++14 actives C++17 support:

but I need a C++14 build

What do you think is different when you build Qt without c++17? The API is the same...

mblanchard

Agreed, but my problem is that the C++17 binaires seems to have a versioned sized delacollators (_ZdlPvm@@Qt5) that the C++14 has not.

Christian Ehrlicher

But how should this be a problem? Do you want to move the compiled binaries to another system? When using the same gcc and linker and compile a program with c++14 on the same system I don't see why it should not work.

Christian Ehrlicher

If you really want to disable it you can at least modify configure.json and remove c++17 from the section "cxx17" / "qmake"

mblanchard

Ok thanks I'll try that!