编译命令成功，链接错误 undefined reference to symbol '_ZNSt3__15mutex4lockEv'

Question

问题：

我现在正在学习 boost asio。当我尝试使用 CMake 在 ubuntu18.04 上编译其示例代码时，我使用了 clang 工具集。我收到链接错误。

undefined reference to symbol '_ZNSt3__15mutex4lockEv'

但如果我尝试使用 clang++ 命令来编译它，它会顺利进行。

clang++ -std=c++2a -stdlib=libc++ -v -fcoroutines-ts -lpthread test.cpp -o test

test.cpp 文件：

#include <boost/asio/co_spawn.hpp>
#include <boost/asio/detached.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/signal_set.hpp>
#include <boost/asio/write.hpp>
#include <cstdio>
using boost::asio::awaitable;
using boost::asio::co_spawn;
using boost::asio::detached;
using boost::asio::use_awaitable;
using boost::asio::ip::tcp;
namespace this_coro = boost::asio::this_coro;

awaitable<void> echo(tcp::socket socket) {
  try {
    char data[1024];
    for (;;) {
      std::size_t n = co_await socket.async_read_some(boost::asio::buffer(data),
                                                      use_awaitable);
      co_await async_write(socket, boost::asio::buffer(data, n), use_awaitable);
    }
  } catch (std::exception &e) {
    std::printf("echo Exception: %s\n", e.what());
  }
}

awaitable<void> listener() {
  auto executor = co_await this_coro::executor;
  tcp::acceptor acceptor(executor, {tcp::v4(), 55555});
  for (;;) {
    tcp::socket socket = co_await acceptor.async_accept(use_awaitable);
    co_spawn(
        executor,
        [socket = std::move(socket)]() mutable {
          return echo(std::move(socket));
        },
        detached);
  }
}

int main() {
  try {
    boost::asio::io_context io_context(1);

    boost::asio::signal_set signals(io_context, SIGINT, SIGTERM);
    signals.async_wait([&](auto, auto) { io_context.stop(); });

    co_spawn(io_context, listener, detached);

    io_context.run();
  } catch (std::exception &e) {
    std::printf("Exception: %s\n", e.what());
  }
}

CMakeLists.txt：

project(learn)

cmake_minimum_required(VERSION 3.11)

find_package(Boost 1.72.0 COMPONENTS fiber context thread)
if(Boost_FOUND)
    set(Boost_USE_MULTITHREAD ON)
    include_directories(${Boost_INCLUDE_DIRS})
    link_libraries(${Boost_LIBRARIES})
endif()

if(MSVC)
    set(CMAKE_CXX_STANDARD 17)
    add_compile_options(/await)
else()
    add_compile_options("-std=c++2a" "-stdlib=libc++" "-v" "-fcoroutines-ts")
endif()

#add_executable(learn_asio learn_asio.cpp)
add_executable(test test.cpp)

编译输出：

 cd /mnt/e/c++/learn/out/build/WSL-Clang-Debug;export CFLAGS=-fno-limit-debug-info;export CXXFLAGS=-fno-limit-debug-info;/usr/bin/cmake --build /mnt/e/c++/learn/out/build/WSL-Clang-Debug --clean-first  ;

[ 50%] Building CXX object CMakeFiles/test.dir/test.cpp.o
clang version 9.0.0-2~ubuntu18.04.2 (tags/RELEASE_900/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.4.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.4.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
 "/usr/lib/llvm-9/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name test.cpp -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debug-info-kind=standalone -dwarf-version=4 -debugger-tuning=gdb -v -coverage-notes-file /mnt/e/c++/learn/out/build/WSL-Clang-Debug/CMakeFiles/test.dir/test.cpp.gcno -resource-dir /usr/lib/llvm-9/lib/clang/9.0.0 -D BOOST_ALL_NO_LIB -D BOOST_CONTEXT_DYN_LINK -D BOOST_FIBER_DYN_LINK -D BOOST_FILESYSTEM_DYN_LINK -D BOOST_THREAD_DYN_LINK -internal-isystem /usr/lib/llvm-9/bin/../include/c++/v1 -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-9/lib/clang/9.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++2a -fdeprecated-macro -fdebug-compilation-dir /mnt/e/c++/learn/out/build/WSL-Clang-Debug -ferror-limit 19 -fmessage-length 0 -fcoroutines-ts -fno-implicit-modules -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -faddrsig -o CMakeFiles/test.dir/test.cpp.o -x c++ /mnt/e/c++/learn/test.cpp
clang -cc1 version 9.0.0 based upon LLVM 9.0.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/llvm-9/bin/../include/c++/v1
 /usr/local/include
 /usr/lib/llvm-9/lib/clang/9.0.0/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
[100%] Linking CXX executable test
/usr/bin/ld: CMakeFiles/test.dir/test.cpp.o: undefined reference to symbol '_ZNSt3__15mutex4lockEv'
//usr/lib/x86_64-linux-gnu/libc++.so.1: error adding symbols: DSO missing from command line
clang: error: linker command failed with exit code 1 (use -v to see invocation)
CMakeFiles/test.dir/build.make:87: recipe for target 'test' failed
make[2]: *** [test] Error 1
CMakeFiles/Makefile2:75: recipe for target 'CMakeFiles/test.dir/all' failed
make[1]: *** [CMakeFiles/test.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

链接错误：

/usr/bin/ld: CMakeFiles/test.dir/test.cpp.o: undefined reference to symbol '_ZNSt3__15mutex4lockEv'
//usr/lib/x86_64-linux-gnu/libc++.so.1: error adding symbols: DSO missing from command line
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

不确定，我认为错误的原因在 CMakeLists.txt 中：

add_compile_options("-std=c++2a" "-stdlib=libc++" "-v" "-fcoroutines-ts")

-stdlib=libc++不是编译器选项，是链接器选项，所以没有使用，可以在编译结果中看到。用下面两行更新这一行：

add_compile_options("-std=c++2a" "-v" "-fcoroutines-ts")
add_link_options("-stdlib=libc++")

我希望它会有所帮助。