如何使用 cmake 包含静态库？

Question

我想添加库 ixwebsocket 我的项目。按照库的说明，我得到了 libixwebsocket.a （编译后的静态库，如果我错了请纠正我）。我如何在我的项目中使用这个 .a 文件？

为了测试，我创建了以下程序：main.cpp

#CMakeLists.txt
cmake_minimum_required(VERSION 3.0.0)
project(cpptest VERSION 0.1.0)

include(CTest)
enable_testing()

add_executable(cpptest main.cpp)

set(CPACK_PROJECT_NAME ${PROJECT_NAME})
set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
include(CPack)

target_link_libraries(cpptest "${CMAKE_SOURCE_DIR}/libixwebsocket.a")

//main.cpp
#include <iostream>
#include <ixwebsocket/IXNetSystem.h>
#include <ixwebsocket/IXWebSocket.h>

int main(int, char**) {
    std::cout << "Hello, world!\n";

    ix::WebSocket webSocket;
}

在目录中我有 CMakeLists.txt、libixwebsocket.a 和 main.cpp。

我得到一长串 未定义引用 错误，第一个 :

[build] [ 50%] Linking CXX executable cpptest
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocket.cpp.o): in function `ix::WebSocket::start()':
[build] IXWebSocket.cpp:(.text+0x2240): undefined reference to `pthread_create'
ld] /usr/bin/ld: ../libixwebsocket.a(IXWebSocket.cpp.o): in function `ix::WebSocket::checkConnection(bool)':
[build] IXWebSocket.cpp:(.text+0x5b8d): undefined reference to `pthread_cond_clockwait'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `bool ix::WebSocketPerMessageDeflateCompressor::compressData<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&) [clone .part.0]':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x67): undefined reference to `deflate'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateCompressor::~WebSocketPerMessageDeflateCompressor()':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x35c): undefined reference to `deflateEnd'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateCompressor::init(unsigned char, bool)':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x3a6): undefined reference to `deflateInit2_'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateDecompressor::~WebSocketPerMessageDeflateDecompressor()':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x64c): undefined reference to `inflateEnd'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateDecompressor::init(unsigned char, bool)':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x685): undefined reference to `inflateInit2_'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateDecompressor::decompress(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&)':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x7d6): undefined reference to `inflate'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `bool ix::WebSocketPerMessageDeflateCompressor::compressData<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<unsigned char, std::allocator<unsigned char> > >(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::vector<unsigned char, std::allocator<unsigned char> >&) [clone .part.0]':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x90d): undefined reference to `deflate'
[build] /usr/bin/ld: ../libixwebsocket.a(IXSocketOpenSSL.cpp.o): in function `ix::SocketOpenSSL::openSSLInitialize()':
[build] IXSocketOpenSSL.cpp:(.text+0x1c): undefined reference to `OPENSSL_init_ssl'
[build] /usr/bin/ld: IXSocketOpenSSL.cpp:(.text+0x29): undefined reference to `OPENSSL_init_ssl'

如何解决这些未定义的引用错误？提前致谢！

Answer 1

我运行今天遇到了类似的问题，库链接得很好，但是静态库只是 .o 文件的集合，并且不了解它自己的依赖关系...

这个命令对我有用：

g++ -o output/myapp -std=c++17 myapp.cpp -Llib -framework CoreFoundation -framework Security -lmylib

我不是 CMake 专家，但 this answer 似乎表明下面的方法可以达到相同的效果

target_link_libraries(program "-framework CoreFoundation" "-framework Security")

因此，如果我们将其应用于您的案例：

#CMakeLists.txt
cmake_minimum_required(VERSION 3.0.0)
project(cpptest VERSION 0.1.0)

include(CTest)
enable_testing()

add_executable(cpptest main.cpp)

set(CPACK_PROJECT_NAME ${PROJECT_NAME})
set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
include(CPack)

target_link_libraries(cpptest "${CMAKE_SOURCE_DIR}/libixwebsocket.a" "-framework CoreFoundation")

我感觉 pthread_create 很可能住在 CoreFoundation 中，但我只是猜测...您可能需要尝试一些框架才能找到合适的框架。

希望对您有所帮助:)

Answer 2

最好使用 find_package() 调用。这样你就可以确保库确实安装在你的系统上，或者在构建树中导出。

如果您的系统上安装了库，您可以使用此调用，如下所示：

find_package(ixwebsocket REQUIRED)
target_link_libraries(cpptest ixwebsocket::ixwebsocket)

在你的情况下，由于库是独立编译的（并且它不是你的树中的目标），你需要使用 find_library(IXWEBSOCKET_LIB ixwebsocket) 并指定额外的 hints/names 如果你有库您自己的位置，关注 the docs.

如何使用 cmake 包含静态库？

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