【CMake】Your C++ compiler does NOT fully support C++17

项目场景：

编译YouCompleteMe时，遇到C++编译器不支持C++17，导致编译失败。

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问题描述

• 出错的关键日志

-- The C compiler identification is GNU 4.8.5
-- The CXX compiler identification is GNU 4.8.5
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:232 (message):
  Your C++ compiler does NOT fully support C++17.


-- Configuring incomplete, errors occurred!
See also "/tmp/ycm_build_ym0u6oos/CMakeFiles/CMakeOutput.log".

•  gcc-11.2.0 已安装并且支持C++17，但不是安装在/usr/bin/目录下
• 项目执行环境中已配置PATH优先为gcc-11.2.0的安装路径，执行c++显示的是11.2.0（正确）
• 项目执行编译时，依然显示gcc是4.8.5，所以不支持C++17

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原因分析：

通过 查看cmake/CMakeCache.txt 可知，原来，CMake在构建时，通过/usr/bin/c++进行判断其版本号来判断是否支持C++17。

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解决方案：

 清除缓存  CMakeCache.txt，极有可能解决此问题

但最好效的方法是，执行环境中设置下CC和CXX的变量赋值

...

export CC=$(which gcc)
export CXX=$(which g++)
...

类似问题的解决参考

CMake complains about GCC version but newer is installed · Issue #5117 · Project-OSRM/osrm-backend · GitHub