如何消除针对 c++17 功能的 gcc 警告？

Question

I self built gcc 7 to try out some new c++17 features.

When I built the code, I saw hundred lines of warnings, saying certain features are available only when -std=c++1z (I have already specified -std=c++1z in the build command line and I tried gnu++1z too)

I want to silence this warning. when using clang 4, there was an option -Wno-c++1z-extensions

but this option is not recognized by gcc.

Answer 1

I have root caused the reason for my problem.

It's because I set -std=c++17 with cmake. and I also have included Qt5. Qt5 settings overwrote my -std=c++17. With make VERBOSE=1, I could see both -std=c++17 and -std=c++14.

This confuses the compiler.

the problem is related to https://gitlab.kitware.com/cmake/cmake/issues/16468

Answer 2

gcc 12 supports the option to suppress the warning of the specific c++ version

-Wno-c++17-extensions ( work well both on gcc12 and clang)

ref gcc/clang compiling options:

https://docs.adacore.com/live/wave/gcc-12.x/html/gcc/gcc.html#Warning-Options

https://releases.llvm.org/12.0.0/tools/clang/docs/DiagnosticsReference.html#diagnostic-flags

but it's better to support c++17 features through flag:

• -std=c++17
• -std=gnu++17