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c++ - 未编译具有 3rd 方库的子目录

问题描述

我想从这里使用 rpclib 。我开始了一个新项目，main.cpp并将其作为子目录CMakeLists.txt复制到我的项目中：rpclib

我的代码正是 rpclib 中的示例，如下所示：

#include <iostream>
#include "rpc/server.h"

void foo() {
    std::cout << "foo was called!" << std::endl;
}

int main(int argc, char *argv[]) {
    // Creating a server that listens on port 8080
    rpc::server srv(8080);

    // Binding the name "foo" to free function foo.
    // note: the signature is automatically captured
    srv.bind("foo", &foo);

    // Binding a lambda function to the name "add".
    srv.bind("add", [](int a, int b) {
        return a + b;
    });

    // Run the server loop.
    srv.run();

    return 0;
}

我的 CMakeLists.txt 看起来像这样：

cmake_minimum_required(VERSION 3.16)
project(RPC_Test)

set(CMAKE_CXX_STANDARD 14)

add_subdirectory(rpclib)
include_directories(rpclib/include)

add_executable(RPC_Test main.cpp)

据我了解，该行add_subdirectory(rpclib)负责添加 rpclib 并在构建RPC_Test-Project 期间构建其内容。看来，我错了。rpclib 中没有任何内容可以构建，并且构建过程 RPC_Test 失败并出现链接器错误：

/Applications/CLion.app/Contents/bin/cmake/mac/bin/cmake --build /Users/seba/CLionProjects/rpc-cpp/cmake-build-debug-system --target RPC_Test -- -j 3
Scanning dependencies of target RPC_Test
[ 50%] Building CXX object CMakeFiles/RPC_Test.dir/main.cpp.o
[100%] Linking CXX executable RPC_Test
Undefined symbols for architecture x86_64:
  "rpc::detail::dispatcher::enforce_arg_count(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, unsigned long, unsigned long)", referenced from:
      void rpc::detail::dispatcher::bind<void (*)()>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, void (*)(), rpc::detail::tags::void_result const&, rpc::detail::tags::zero_arg const&)::'lambda'(clmdep_msgpack::v2::object const&)::operator()(clmdep_msgpack::v2::object const&) const in main.cpp.o
      void rpc::detail::dispatcher::bind<main::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, main::$_0, rpc::detail::tags::nonvoid_result const&, rpc::detail::tags::nonzero_arg const&)::'lambda'(clmdep_msgpack::v2::object const&)::operator()(clmdep_msgpack::v2::object const&) const in main.cpp.o
  "rpc::detail::dispatcher::enforce_unique_name(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)", referenced from:
      void rpc::detail::dispatcher::bind<void (*)()>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, void (*)()) in main.cpp.o
      void rpc::detail::dispatcher::bind<void (*)()>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, void (*)(), rpc::detail::tags::void_result const&, rpc::detail::tags::zero_arg const&) in main.cpp.o
      void rpc::detail::dispatcher::bind<main::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, main::$_0) in main.cpp.o
      void rpc::detail::dispatcher::bind<main::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, main::$_0, rpc::detail::tags::nonvoid_result const&, rpc::detail::tags::nonzero_arg const&) in main.cpp.o
  "rpc::server::run()", referenced from:
      _main in main.cpp.o
  "rpc::server::server(unsigned short)", referenced from:
      _main in main.cpp.o
  "rpc::server::~server()", referenced from:
      _main 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[3]: *** [RPC_Test] Error 1
make[2]: *** [CMakeFiles/RPC_Test.dir/all] Error 2
make[1]: *** [CMakeFiles/RPC_Test.dir/rule] Error 2
make: *** [RPC_Test] Error 2

什么不见​​了？

标签： c++cmake

解决方案

您在targettarget_link_libraries(RPC_Test PRIVATE rpc)的定义之后缺少 a 。这是在's中定义的库目标的名称，而不仅仅是生成的二进制工件的基本名称。RPC_TestrpcrpclibCMakeLists.txt

当使用具有target_link_libraries类似 CMake 的目标名称时，不仅会添加-lrpc到链接器调用中，还会自动添加使用库所需的包含目录，并确保该rpc库是在RPC_Test. 特别是，这意味着您还可以include_directories在使用target_link_libraries(RPC_Test PRIVATE rpc).

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