为什么我不能链接到 boost 的线程库？

Question

我使用的是 Mac OS 10.11，并将 clang 作为我的 C/C++ 编译器。 我用最简单的方式安装了 boost brew install boost

首先我尝试了这些代码

#include <iostream>
#include <boost/array.hpp>

int main() {
    boost::array<int, 4> arr = {1, 2, 3, 4};
    std::cout << arr[3];
    return 0;
}

它可以正常工作。所以看来 boost 的设置是正确的。

但是什么时候尝试使用#include<boost/thread.hpp>，示例代码如下：

#include <boost/thread.hpp>
#include <boost/chrono.hpp>
#include <iostream>

void wait(int seconds)
{
    boost::this_thread::sleep_for(boost::chrono::seconds{seconds});
}

void thread()
{
    for (int i = 0; i < 5; ++i)
    {
        wait(1);
        std::cout << i << '\n';
    }
}

int main()
{
    boost::thread t{thread};
    t.join();
}

然后我得到了这些

/Applications/CLion.app/Contents/bin/cmake/bin/cmake --build /Users/vita-nove/CLionProjects/untitled/cmake-build-debug --target untitled -- -j 4
[ 50%] Linking CXX executable untitled
Undefined symbols for architecture x86_64:
  "boost::this_thread::hidden::sleep_for(timespec const&)", referenced from:
  boost::this_thread::sleep_for(boost::chrono::duration<long long,    boost::ratio<1l, 1000000000l> > const&) in main.cpp.o
  "boost::detail::thread_data_base::~thread_data_base()", referenced from:
  boost::detail::thread_data<void (*)()>::~thread_data() in main.cpp.o
  "boost::system::system_category()", referenced from:
  boost::thread_exception::thread_exception(int, char const*) in main.cpp.o
  ___cxx_global_var_init.2 in main.cpp.o
  "boost::system::generic_category()", referenced from:
  ___cxx_global_var_init in main.cpp.o
  ___cxx_global_var_init.1 in main.cpp.o
  "boost::thread::join_noexcept()", referenced from:
  boost::thread::join() in main.cpp.o
  "boost::thread::native_handle()", referenced from:
  boost::thread::get_id() const in main.cpp.o
  "boost::thread::start_thread_noexcept()", referenced from:
  boost::thread::start_thread() in main.cpp.o
  "boost::thread::detach()", referenced from:
  boost::thread::~thread() in main.cpp.o
  "typeinfo for boost::detail::thread_data_base", referenced from:
  typeinfo for boost::detail::thread_data<void (*)()> in main.cpp.o
  "vtable for boost::detail::thread_data_base", referenced from:
  boost::detail::thread_data_base::thread_data_base() in main.cpp.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[3]: *** [untitled] Error 1
make[2]: *** [CMakeFiles/untitled.dir/all] Error 2
make[1]: *** [CMakeFiles/untitled.dir/rule] Error 2
make: *** [untitled] Error 2

我在谷歌上搜索了一段时间。我试图设置库目录set(Boost_LIBRARY_DIRS /usr/local/lib) link_directories(${Boost_LIBRARY_DIRS})。

我的 CMakeLists.txt 在这里：

cmake_minimum_required(VERSION 3.7)
project(untitled)

set(CMAKE_CXX_STANDARD 14)

set(SOURCE_FILES main.cpp)
add_executable(untitled main.cpp)
set(Boost_LIBRARY_DIRS /usr/local/lib)
link_directories(${Boost_LIBRARY_DIRS})

我也试过clang++ main.cpp -lboost_thread-mt。 然后得到了这些：

vita-nove@MacBook-Pro:~/CLionProjects/untitled$ clang++ main.cpp -lboost_thread-mt
Undefined symbols for architecture x86_64:
  "boost::system::system_category()", referenced from:
  boost::thread_exception::thread_exception(int, char const*) in main-964777.o
  ___cxx_global_var_init.2 in main-964777.o
  "boost::system::generic_category()", referenced from:
  ___cxx_global_var_init in main-964777.o
  ___cxx_global_var_init.1 in main-964777.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

谁能帮帮我？非常感谢！

---

更新： 正如@Angew 所说，使用 find_package 命令，我遇到了一些新错误。

/Applications/CLion.app/Contents/bin/cmake/bin/cmake --build /Users/vita-nove/CLionProjects/untitled/cmake-build-debug --target untitled -- -j 4
CMake Warning at /Applications/CLion.app/Contents/bin/cmake/share/cmake-3.7/Modules/FindBoost.cmake:744 (message):
  Imported targets not available for Boost version 106300
Call Stack (most recent call first):
  /Applications/CLion.app/Contents/bin/cmake/share/cmake-3.7/Modules/FindBoost.cmake:848 (_Boost_COMPONENT_DEPENDENCIES)
  /Applications/CLion.app/Contents/bin/cmake/share/cmake-3.7/Modules/FindBoost.cmake:1435 (_Boost_MISSING_DEPENDENCIES)
  CMakeLists.txt:9 (find_package)


-- Boost version: 1.63.0
-- Found the following Boost libraries:
--   thread
-- Configuring done
CMake Error at CMakeLists.txt:7 (add_executable):
  Target "untitled" links to target "Boost::thread" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?


-- Generating done
-- Build files have been written to: /Users/vita-nove/CLionProjects/untitled/cmake-build-debug
make: *** [cmake_check_build_system] Error 1

---

更新

我尝试了一些旧版本的 boost，但还是一样。 如果我使用target_include_directories(untitled PRIVATE ${Boost_INCLUDE_DIRS}) 和target_link_libraries(untitled ${Boost_LIBRARIES})

Scanning dependencies of target untitled
[ 50%] Building CXX object CMakeFiles/untitled.dir/main.cpp.o
[100%] Linking CXX executable untitled
Undefined symbols for architecture x86_64:
  "boost::system::system_category()", referenced from:
  boost::thread_exception::thread_exception(int, char const*) in main.cpp.o
  ___cxx_global_var_init.2 in main.cpp.o
  "boost::system::generic_category()", referenced from:
  ___cxx_global_var_init in main.cpp.o
  ___cxx_global_var_init.1 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]: *** [untitled] Error 1
make[1]: *** [CMakeFiles/untitled.dir/all] Error 2
make: *** [all] Error 2

---

更新

@Angew 找到了真正的答案。

我再次更新了答案。看来 Boost.Thread 也要求您使用 Boost.System 。这将由导入的目标处理，但由于您不能使用这些，显然您必须明确请求它。

find_package(Boost REQUIRED COMPONENTS thread system) 让它工作正常。

Answer 1

与第三方包交互的正确 CMake 方法是使用 find_package() 调用，它将使用查找模块（随 CMake 提供）或包配置文件（由第三方包提供） , 以找到必要的库、目录等。

对于 Boost，CMake 本身附带了一个查找模块。它提供了一个非常可调的接口，您可以阅读它的documentation 了解详细信息。但是，这是您可以使用它的最基本方式：

cmake_minimum_required(VERSION 3.7)
project(untitled)

set(CMAKE_CXX_STANDARD 14)

find_package(Boost REQUIRED COMPONENTS thread)
add_executable(untitled main.cpp)
target_link_libraries(untitled Boost::thread)

---

根据您收到的这条消息：

导入的目标不适用于 Boost 版本 106300

您的 Boost 版本似乎无法使用导入目标方法。因此，您将不得不回退到 find 模块提供的变量：

cmake_minimum_required(VERSION 3.7)
project(untitled)

set(CMAKE_CXX_STANDARD 14)

find_package(Boost REQUIRED COMPONENTS thread system)

add_executable(untitled main.cpp)
target_include_directories(untitled PRIVATE ${Boost_INCLUDE_DIRS})
target_link_libraries(untitled ${Boost_LIBRARIES})