如何在 CMake 的 try

本文介绍了如何在 CMake 的 try_compile 函数中为 OpenMP 设置链接器标志的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我想验证当前编译器是否可以使用 openmp 支持进行构建.该应用程序确实部署在各种 unix 系统上，其中一些可能有旧版本的 OpenMP，我想测试重要的 OpenMP 功能.所以，我想构建一个包含一些 OpenMP 调用的测试源文件.

I would like to verify that the current compiler can build with openmp support. The application has do deploy across a wide variety of unix systems, some of which might have old versions of OpenMP, and I would like to test for important OpenMP functionality. So, I want to build a test source file that incorporates some of the OpenMP calls.

因此，我创建了一个非常简单的测试文件，并尝试使用 CMake 中的 try_compile 函数.不幸的是，它似乎没有正确应用 -fopenmp 链接器标志.有谁知道如何强制链接器标志或查看链接器标志是否在任何地方应用?

Thus, I created a very simple test file, and attempted to use the try_compile function from CMake. Ufortunately, it doesn't seem to apply the -fopenmp linker flag correctly. Does anyone know how to either force the linker flag or to see if the linker flag is being applied anywhere?

来自 CMakeLists.txt

from CMakeLists.txt

try_compile(
    HAVE_OPENMP
    ${APBS_ROOT}/src/config
    ${APBS_ROOT}/src/config/omp_test.c
    CMAKE_FLAGS "-DCMAKE_C_FLAGS=-fopenmp -DCMAKE_EXE_LINKER_FLAGS=-fopenmp"
    OUTPUT_VARIABLE TRY_COMPILE_OUTPUT
    )

来自 omp_test.c

from omp_test.c

#include <stdio.h>
#include <omp.h>

int main()
{
    int i;
    int threadID = 0;
    #pragma omp parallel for private(i, threadID)
    for(i = 0; i < 16; i++ )
    {
        threadID = omp_get_thread_num();
        #pragma omp critical
        {
            printf("Thread %d reporting
", threadID);
        }
    }
    return 0;
}

结果输出是

Change Dir: src/config/CMakeFiles/CMakeTmp

Run Build Command:/usr/bin/make "cmTryCompileExec/fast"
/usr/bin/make -f CMakeFiles/cmTryCompileExec.dir/build.make CMakeFiles/cmTryCompileExec.dir/build
make[1]: Entering directory `src/config/CMakeFiles/CMakeTmp'
/usr/bin/cmake -E cmake_progress_report /data/work/source/apbs/src/config/CMakeFiles/CMakeTmp/CMakeFiles 1
Building C object CMakeFiles/cmTryCompileExec.dir/omp_test.c.o
/usr/bin/gcc    -o CMakeFiles/cmTryCompileExec.dir/omp_test.c.o   -c /data/work/source/apbs/src/config/omp_test.c
Linking C executable cmTryCompileExec
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTryCompileExec.dir/link.txt --verbose=1
/usr/bin/gcc         CMakeFiles/cmTryCompileExec.dir/omp_test.c.o  -o cmTryCompileExec -rdynamic 
CMakeFiles/cmTryCompileExec.dir/omp_test.c.o: In function `main':
omp_test.c:(.text+0x19): undefined reference to `omp_get_thread_num'
collect2: ld returned 1 exit status
make[1]: *** [cmTryCompileExec] Error 1
make[1]: Leaving directory `src/config/CMakeFiles/CMakeTmp'
make: *** [cmTryCompileExec/fast] Error 2

CMake Error at CMakeLists.txt:688 (message):
  Test OpenMP program would not build.  OpenMP disabled

当我尝试在命令行上编译测试程序时，它工作正常

When I try to compile the test program on the command line, it works fine

src/config$ gcc -fopenmp omp_test.c -o omp_test && ./omp_test
Thread 1 reporting
Thread 4 reporting
Thread 7 reporting
Thread 11 reporting
Thread 9 reporting
Thread 12 reporting
Thread 6 reporting
Thread 8 reporting
Thread 15 reporting
Thread 13 reporting
Thread 10 reporting
Thread 0 reporting
Thread 3 reporting
Thread 2 reporting
Thread 5 reporting
Thread 14 reporting

推荐答案

CMake 有一个 标准模块，用于测试编译器是否支持OpenMP:

CMake has a standard module for testing if the compiler supports OpenMP:

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()

注意:
不建议再使用此答案将 OpenMP 包含在当前 CMake 版本的项目中.参考其他答案.

Note:
This answer is not recommended to be used anymore for including OpenMP in the project for current CMake versions. Refer to the other answers.

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