找不到以下 Boost 库：boost_asio

Question

当我尝试编译使用 boost 和 asio 的 cmake 项目时，make出现以下错误：

CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `__cxx_global_var_init1':
/usr/include/boost/system/error_code.hpp:222: undefined reference to `boost::system::generic_category()'    CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `__cxx_global_var_init1':
/usr/include/boost/system/error_code.hpp:222: undefined reference to `boost::system::generic_category()'
CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `__cxx_global_var_init2':
/usr/include/boost/system/error_code.hpp:223: undefined reference to `boost::system::generic_category()'
CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `__cxx_global_var_init3':
/usr/include/boost/system/error_code.hpp:224: undefined reference to `boost::system::system_category()'
CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `boost::asio::error::get_system_category()':
/usr/include/boost/asio/error.hpp:216: undefined reference to `boost::system::system_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `__cxx_global_var_init1':
/usr/include/boost/system/error_code.hpp:222: undefined reference to `boost::system::generic_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `__cxx_global_var_init2':
/usr/include/boost/system/error_code.hpp:223: undefined reference to `boost::system::generic_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `__cxx_global_var_init3':
/usr/include/boost/system/error_code.hpp:224: undefined reference to `boost::system::system_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `boost::network::uri::uri::parse()':
/home/darren/373project/include/boost/network/uri/uri.hpp:178: undefined reference to `boost::network::uri::detail::parse(__gnu_cxx::__normal_iterator<char const*, std::string>, __gnu_cxx::__normal_iterator<char const*, std::string>, boost::network::uri::detail::uri_parts<__gnu_cxx::__normal_iterator<char const*, std::string> >&)'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `error_code':
/usr/include/boost/system/error_code.hpp:323: undefined reference to `boost::system::system_category()'
CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `__cxx_global_var_init2':
/usr/include/boost/system/error_code.hpp:223: undefined reference to `boost::system::generic_category()'
CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `__cxx_global_var_init3':
/usr/include/boost/system/error_code.hpp:224: undefined reference to `boost::system::system_category()'
CMakeFiles/client-network-handler-test.dir/main.cpp.o: In function `boost::asio::error::get_system_category()':
/usr/include/boost/asio/error.hpp:216: undefined reference to `boost::system::system_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `__cxx_global_var_init1':
/usr/include/boost/system/error_code.hpp:222: undefined reference to `boost::system::generic_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `__cxx_global_var_init2':
/usr/include/boost/system/error_code.hpp:223: undefined reference to `boost::system::generic_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `__cxx_global_var_init3':
/usr/include/boost/system/error_code.hpp:224: undefined reference to `boost::system::system_category()'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `boost::network::uri::uri::parse()':
/home/myUserName/373project/include/boost/network/uri/uri.hpp:178: undefined reference to `boost::network::uri::detail::parse(__gnu_cxx::__normal_iterator<char const*, std::string>, __gnu_cxx::__normal_iterator<char const*, std::string>, boost::network::uri::detail::uri_parts<__gnu_cxx::__normal_iterator<char const*, std::string> >&)'
../../lib/libclient-network-handler.a(ClientNetworkHandler.cpp.o): In function `error_code':
/usr/include/boost/system/error_code.hpp:323: undefined reference to `boost::system::system_category()'

我认为无法找到 asio 库。所以我将此行添加到我的根 CMakeLists.txt：

find_package(Boost 1.54.0 REQUIRED)

并且 CMake 可以找到所有相关的库，如构建日志的这一部分所示：

-- Found the following Boost libraries:
--   unit_test_framework
--   system
--   regex
--   date_time
--   thread
--   filesystem
--   program_options
--   chrono
--   atomic

但是编译仍然会产生列出的第一个错误。当我将该 CMake 行更改为：

find_package(Boost 1.54.0 REQUIRED asio)

我从 CMake 收到此消息：

CMake Error at /usr/share/cmake-2.8/Modules/FindBoost.cmake:1131 (message):
  Unable to find the requested Boost libraries.

  Boost version: 1.54.0

  Boost include path: /usr/include

  Could not find the following Boost libraries:

          boost_asio

如您所见，我安装了所有 Boost 库，但我不明白为什么找不到 asio。

Answer 1

Boost.Asio 是一个只有头文件的库 - 即它不需要链接到您的应用程序。

来自CMakeFindBoost模块的文档：

该模块查找头文件和请求的组件库

（强调我的）。

换句话说，find_package(Boost ...)应该只用于查找非头文件的 Boost 库，如Boost docs 中所列。

从您的链接器错误来看，您似乎确实需要链接 Boost.System：

find_package(Boost 1.54.0 REQUIRED system)
target_include_directories(MyExe PRIVATE ${Boost_INCLUDE_DIRS})
target_link_libraries(MyExe ${Boost_LIBRARIES})