CMake：检查静态 C++ 库的可用性

Question

我正在尝试静态链接多线程二进制文件。如果 CMake 可以警告缺少静态库，那就太好了。

注意：我知道解决方案是安装静态库（Fedora 31 中的 libstdc++-static 和 glibc-static，如果这对任何人都有帮助的话），我只希望 CMake 报告丢失的库和不是在构建时。

（顺便说一句，有没有更好的方法来支持静态链接？目前我有一些平台相关的东西可以在我们的目标系统中支持它，我还没有发现任何更便携的东西......）

这是一个示例 CMakeLists.txt：

cmake_minimum_required(VERSION 3.17)

project(test)

set(CMAKE_CXX_STANDARD 17)

add_link_options(-static)
find_package(Threads REQUIRED)

add_executable(test)
target_link_libraries(test PRIVATE Threads::Threads)

target_sources(test PRIVATE test.cpp)

这是输出：

$ cmake ..
-- The C compiler identification is GNU 9.3.1
-- The CXX compiler identification is GNU 9.3.1
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /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: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ - works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE  
-- Configuring done
-- Generating done
-- Build files have been written to: /home/sergio/src/static_cmake/build
$ make
Scanning dependencies of target test
[ 50%] Linking CXX executable test
/usr/bin/ld: cannot find -lpthread
/usr/bin/ld: cannot find -lstdc++
/usr/bin/ld: cannot find -lm
/usr/bin/ld: cannot find -lc
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/test.dir/build.make:101: test] Error 1
make[1]: *** [CMakeFiles/Makefile2:93: CMakeFiles/test.dir/all] Error 2
make: *** [Makefile:101: all] Error 2

Answer 1

正如所评论的，在 CMake 中（在编译/链接之前）为缺少的库产生错误的一种方法是使用 find_library()。如果CMake找不到具体的库，使用库变量时会报错：

# Define a variable my_pthread_static_lib to store the library, if found.
find_library(my_pthread_static_lib libpthread.a)

add_executable(test)
# Error will occur here during CMake configuration, if not found
target_link_libraries(test PRIVATE ${my_pthread_static_lib})

如果找不到my_pthread_static_lib库，就会出现这个错误：

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
my_pthread_static_lib
    linked by target "test" in directory /path/to/CMake/file