My project directory is as follows:
<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
And CMakeLists.txt file is as follows:
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)
As expected, CMake generates the following precompiled header files in build/CMakeFiles/MyProject.dir/ :
cmake_pch.c
cmake_pch.cxx
cmake_pch.cxx.obj
cmake_pch_cxx.pch
cmake_pch.h
cmake_pch.hxx
I am using this CMake project in Visual Studio 2019, and when I try to run main.cpp, Visual Studio gives me a bunch of errors, such as:
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
When I searched error code C4233 online, I learned that it is because a C code is trying to be compiled as a C++ code. Also, build process from Visual Studio (I guess uses ninja) shows that:
[1/33] Building C object CMakeFiles\MyProject.dir\cmake_pch.c.obj
Hence, I guess it tries to build my precompiled header as a c source, instead it is a C++ source. I also tried to change the pch extension to .hpp but it didn't work either. How can I specify CMake to mark precompiled header as C++ (or I guess CXX) source instead of pure C?
EDIT: When I disable the target_precompile_headers
the program runs fine, hence I am certain that this is a precompiled header issue.
Thanks to @drescherjm, adding target_precompile_headers(${PROJECT_NAME} PRIVATE "$<$<COMPILE_LANGUAGE:CXX>:${CMAKE_SOURCE_DIR}/MyProject/pch.h>"
got rid of the errors.