我可以生成我的CMake项目，但我无法构建它。
我有一个相当简单的项目结构：
├── bin
├── build
├── CMakeLists.txt
├── include
│ └── project
│ ├── base_socket.h
│ ├── tcp_client.h
│ ├── tcp_server.h
│ ├── udp_client.h
│ └── udp_server.h
├── LICENSE.txt
├── README.md
└── src
└── project
├── base_socket.cpp
├── CMakeLists.txt
├── main.cpp
├── tcp_client.cpp
├── tcp_server.cpp
├── udp_client.cpp
└── udp_server.cpp
顶级目录中的一个相当直接的CMakeLists.txt文件：
# Project initialization
cmake_minimum_required(VERSION 2.7.2 FATAL_ERROR)
project("cpp_sockets")
# Add include directory
include_directories(include)
# Add subdirectories
add_subdirectory(src/project)
src/project/CmakeLists.txt中的一个相当简单的一个：
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_SOURCE_DIR}/bin)
set(HEADER_DIR ${CMAKE_SOURCE_DIR}/include/project)
set(HEADER_FILES
${HEADER_DIR}/base_socket.h
${HEADER_DIR}/tcp_client.h
${HEADER_DIR}/tcp_server.h
${HEADER_DIR}/udp_client.h
${HEADER_DIR}/udp_server.h
)
add_executable(cpp_sockets main.cpp ${HEADER_FILES})
当我cd进入/build并输入cmake ..时，它可以正常工作。
但是，当我使用make时，我会遇到很多关于undefined reference的可怕错误。
main.cpp:(.text+0x2c6): undefined reference to `UDPClient::UDPClient(int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
main.cpp:(.text+0x2eb): undefined reference to `UDPClient::send_message(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
main.cpp:(.text+0x359): undefined reference to `UDPServer::UDPServer(int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
main.cpp:(.text+0x380): undefined reference to `UDPServer::socket_bind()'
main.cpp:(.text+0x38c): undefined reference to `UDPServer::listen()'
main.cpp:(.text+0x400): undefined reference to `TCPClient::TCPClient(int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
main.cpp:(.text+0x40c): undefined reference to `TCPClient::make_connection()'
main.cpp:(.text+0x42b): undefined reference to `TCPClient::send_message(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
main.cpp:(.text+0x492): undefined reference to `TCPServer::TCPServer(int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
main.cpp:(.text+0x4b9): undefined reference to `TCPServer::socket_bind()'
CMakeFiles/cpp_sockets.dir/main.cpp.o: In function `UDPClient::~UDPClient()':
main.cpp:(.text._ZN9UDPClientD2Ev[_ZN9UDPClientD5Ev]+0x14): undefined reference to `Socket::~Socket()'
CMakeFiles/cpp_sockets.dir/main.cpp.o: In function `UDPServer::~UDPServer()':
main.cpp:(.text._ZN9UDPServerD2Ev[_ZN9UDPServerD5Ev]+0x14): undefined reference to `Socket::~Socket()'
CMakeFiles/cpp_sockets.dir/main.cpp.o: In function `TCPClient::~TCPClient()':
main.cpp:(.text._ZN9TCPClientD2Ev[_ZN9TCPClientD5Ev]+0x14): undefined reference to `Socket::~Socket()'
CMakeFiles/cpp_sockets.dir/main.cpp.o: In function `TCPServer::~TCPServer()':
main.cpp:(.text._ZN9TCPServerD2Ev[_ZN9TCPServerD5Ev]+0x14): undefined reference to `Socket::~Socket()'
collect2: error: ld returned 1 exit status
src/project/CMakeFiles/cpp_sockets.dir/build.make:94: recipe for target '../bin/cpp_sockets' failed
make[2]: *** [../bin/cpp_sockets] Error 1
CMakeFiles/Makefile2:85: recipe for target 'src/project/CMakeFiles/cpp_sockets.dir/all' failed
make[1]: *** [src/project/CMakeFiles/cpp_sockets.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
main.cpp文件如下：
#include "project/udp_server.h"
#include "project/udp_client.h"
#include "project/tcp_client.h"
为什么链接器无法找到这样的引用？
答案 0 :(得分：1)
您的src/project/CMakeLists.txt似乎忽略了将其他cpp文件（例如udp_server.cpp和udp_client.cpp）指定为可执行文件cpp_sockets的依赖项。你需要这样做才能让CMake编译那些源文件;因为你已经包含了相应的标题，它不会自动计算出来进行编译。事实上，add_executable声明不需要对标题说任何内容，因为include_directories命令会处理这个问题。
鉴于main.cpp所依赖的标头文件，其add_executable行应如下所示：
add_executable(cpp_sockets main.cpp udp_server.cpp udp_client.cpp tcp_client.cpp)