CMake 使用 C 風格的預編譯頭文件代替 C++ 版本的預編譯 header

Question

我的項目目錄如下：

<PROJECT-ROOT>:
    - build
    - MyProject:
        - src:
            - main.cpp
            - hello.h (basic file that contains a simple function that prints something using iostream)
        - pch.h (precompiled header)
    - CMakeLists.txt

而CMakeLists.txt文件如下：

cmake_minimum_required(VERSION 3.16)
project(MyProject)

if(MSVC)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")
else()
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wpedantic -std=c++11")
endif()

include_directories(
                    MyProject
                    MyProject/src
)


add_executable(${PROJECT_NAME} ${CMAKE_SOURCE_DIR}/MyProject/pch.h 
                               ${CMAKE_SOURCE_DIR}/MyProject/src/main.cpp
                               ${CMAKE_SOURCE_DIR}/MyProject/src/hello.h)
target_precompile_headers(${PROJECT_NAME} PRIVATE ${CMAKE_SOURCE_DIR}/MyProject/pch.h)

正如預期的那樣，CMake 在 build/CMakeFiles/MyProject.dir/ 中生成以下預編譯的 header 文件：

cmake_pch.c
cmake_pch.cxx
cmake_pch.cxx.obj
cmake_pch_cxx.pch
cmake_pch.h
cmake_pch.hxx

我在 Visual Studio 2019 中使用這個 CMake 項目，當我嘗試運行 main.cpp 時，Visual Studio 給了我一堆錯誤，例如：

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(23): error C2061: syntax error: identifier 'noexcept'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(23): error C2059: syntax error: ';'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(23): error C2449: found '{' at file scope (missing function header?)
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(25): error C2059: syntax error: '}'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(31): error C2061: syntax error: identifier 'noexcept'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(31): error C2059: syntax error: ';'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(31): error C2449: found '{' at file scope (missing function header?)
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstdlib(33): error C2059: syntax error: '}'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\xtr1common(19): error C2061: syntax error: identifier 'std'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\xtr1common(19): error C2059: syntax error: ';'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\xtr1common(19): error C2449: found '{' at file scope (missing function header?)
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\xtr1common(235): error C2059: syntax error: '}'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\iosfwd(175): warning C4157: pragma was ignored by C compiler
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\iosfwd(180): warning C4157: pragma was ignored by C compiler
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(307): error C4233: nonstandard extension used: '__is_union' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(310): error C4233: nonstandard extension used: '__is_union' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(313): error C4233: nonstandard extension used: '__is_class' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(316): error C4233: nonstandard extension used: '__is_class' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(325): error C4233: nonstandard extension used: '__is_convertible_to' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(330): error C4233: nonstandard extension used: '__is_convertible_to' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(359): error C4233: nonstandard extension used: '__is_enum' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(362): error C4233: nonstandard extension used: '__is_enum' keyword only supported in C++, not C
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\type_traits(499): error C4233: nonstandard extension used: '__is_pod' keyword only supported in C++, not C

當我在網上搜索錯誤代碼 C4233 時，得知這是因為 C 代碼試圖編譯為 C++ 代碼。 此外，Visual Studio 的構建過程（我猜是使用 ninja）表明：

[1/33] Building C object CMakeFiles\MyProject.dir\cmake_pch.c.obj

因此，我猜它試圖將我的預編譯 header 構建為 c 源，而不是 C++ 源。 我也嘗試將 pch 擴展名更改為.hpp，但它也不起作用。 如何指定 CMake 將預編譯的 header 標記為 C++ （或者我猜是 CXX）源而不是純 Z341261F8ZB83701FCAD4？

編輯：當我禁用target_precompile_headers程序運行良好，因此我確定這是一個預編譯的 header 問題。

Answer 1

感謝@drescherjm，添加target_precompile_headers(${PROJECT_NAME} PRIVATE "$<$<COMPILE_LANGUAGE:CXX>:${CMAKE_SOURCE_DIR}/MyProject/pch.h>"擺脫了錯誤。