Question

我一直在尝试使用CLion IDE在OpenMP上使用AppleClang编译一个简单的Mac OS X 10.14.5 Mojave程序。

main.cpp：

#include <omp.h>
#include <iostream>

int main() {
    std::cout << omp_get_max_threads() << std::endl;
    return 1;
}

CMakeLists.txt：

cmake_minimum_required(VERSION 3.14)
project(OpenMPTest)

set(CMAKE_CXX_STANDARD 17)

add_executable(OpenMPTest main.cpp)

find_package(OpenMP)
if (OPENMP_FOUND)
    set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
    set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}")
endif()

CMake输出：

/Applications/CLion.app/Contents/bin/cmake/mac/bin/cmake -DCMAKE_BUILD_TYPE=Debug -G "CodeBlocks - Unix Makefiles" /Users/bully/CLionProjects/OpenMPTest
-- The C compiler identification is AppleClang 10.0.1.10010046
-- The CXX compiler identification is AppleClang 10.0.1.10010046
-- Check for working C compiler: /Library/Developer/CommandLineTools/usr/bin/cc
-- Check for working C compiler: /Library/Developer/CommandLineTools/usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found OpenMP_C: -Xclang -fopenmp (found version "3.1") 
-- Found OpenMP_CXX: -Xclang -fopenmp (found version "3.1") 
-- Found OpenMP: TRUE (found version "3.1")  
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/bully/CLionProjects/OpenMPTest/cmake-build-debug

构建项目时，收到链接器错误：

====================[ Build | all | Debug ]=====================================
/Applications/CLion.app/Contents/bin/cmake/mac/bin/cmake --build /Users/bully/CLionProjects/OpenMPTest/cmake-build-debug --target all -- -j 2
Scanning dependencies of target OpenMPTest
[ 50%] Building CXX object CMakeFiles/OpenMPTest.dir/main.cpp.o
[100%] Linking CXX executable OpenMPTest
Undefined symbols for architecture x86_64:
  "_omp_get_max_threads", referenced from:
      _main in main.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [OpenMPTest] Error 1
make[1]: *** [CMakeFiles/OpenMPTest.dir/all] Error 2
make: *** [all] Error 2

这怎么不起作用？使用clang++ main.cpp -lomp安装库头之后，可以从命令行成功运行open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg。

message(STATUS "Linker flags:" "${OpenMP_EXE_LINKER_FLAGS}")打印：

-- Linker flags:

如果我用链接工作将CMAKE_EXE_LINKER_FLAGS的setter替换为set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -lomp")的编译器。为什么我必须手动指定？使它以独立于平台的方式工作的首选方式是什么？ -fopenmp产生clang: error: unsupported option '-fopenmp'。 gcc和MSVC上的Linux和Windows在CMake OpenMP配置下表现不错，但Mac OS X却没有。

Answer 1

Tsyvarev评论说，解决方法是使用"updated" way，其中将OpenMP包含在CMake中：

cmake_minimum_required(VERSION 3.14)
project(OpenMPTest)

set(CMAKE_CXX_STANDARD 17)

add_executable(OpenMPTest main.cpp)

find_package(OpenMP REQUIRED) # Find the package
target_link_libraries(${PROJECT_NAME} ${OpenMP_CXX_LIBRARIES}) # Link against it for C++

此代码分别使用其平台的默认编译器在Windows，Ubuntu和Mac OS X上进行编译。

不推荐接受的答案here，尽管它的投票最多。

在Mac OS X Mojave上使用AppleClang对OpenMP进行编译和链接

1 个答案: