如何让 CMake 在 Ubuntu 上识别 pthread?

问题描述

如果我直接在命令行上用 g++ 编译，我可以看到我需要的一切都在那里:

If I compile on the command-line with g++ directly, I can see everything I need is there:

$ g++ -pthread test.cpp
$ ldd a.out
    linux-vdso.so.1 =>  (0x00007fffd05b3000)
    libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f4a1ba8d000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f4a1b870000)
    ...more...

然后我尝试为这个 5 行测试应用程序创建一个简单的 cmake 文件:

Then I try to create a simple cmake file for this 5-line test app:

$ cat CMakeLists.txt 
PROJECT ( Test CXX )
CMAKE_MINIMUM_REQUIRED ( VERSION 2.8 )
FIND_PACKAGE ( Threads REQUIRED )
ADD_EXECUTABLE ( test test.cpp )
TARGET_LINK_LIBRARIES ( test ${CMAKE_THREAD_LIBS_INIT} )

但是，我不明白为什么 CMake 没有找到它需要用于 Threads 的内容:

However, I cannot figure out why CMake doesn't find what it needs to use for Threads:

$ cd build/
$ cmake ..
CMake Error at /usr/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:97 (MESSAGE):
  Could NOT find Threads (missing: Threads_FOUND)
Call Stack (most recent call first):
  /usr/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:288 (_FPHSA_FAILURE_MESSAGE)
  /usr/share/cmake-2.8/Modules/FindThreads.cmake:166 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  CMakeLists.txt:4 (FIND_PACKAGE)
-- Configuring incomplete, errors occurred!

推荐答案

哦，这太痛苦了！我可能为此浪费了 2 个小时.解决办法如下:

Oh, this was was a pain! I probably lost 2 hours on this. Here is the solution:

CMake 使用简短的C"应用程序来测试/尝试事物.如果 CMakeLists.txt 声明项目使用了 C++，而没有列出 C，那么其中一些 shorts 测试错误地失败了，然后 cmake 认为这些东西没有找到.

CMake uses short 'C' applications to test/try things. If the CMakeLists.txt states that C++ is used for the project, without also listing C, then some of those shorts tests incorrectly fail, and cmake then thinks those things aren't found.

解决方案是从这里更改 CMakeLists 的第一行:

The solution was to change the first line of CMakeLists from this:

PROJECT ( Test CXX )

...将 C 作为一种语言包含进来:

...to include C as a language:

PROJECT ( Test C CXX )

然后删除build，重新创建它，然后一切正常:

Then delete build, recreate it, and everything then works:

rm -rf build
mkdir build
cd build
cmake ..

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