Question

我正在尝试构建CMake项目，下面是我正在尝试做的示例代码。

我正在开发两个头文件，我想使用线程头从类 Loader 中调用类 Processor 中的成员函数。这是代码，以及CMake，以及运行make命令后收到的错误消息。

CMakeLists.txt

cmake_minimum_required(VERSION 3.2.2)
project(c-plus-assignment)
## C++11 Flags
add_compile_options(-std=c++11)
add_compile_options(-pthread)
add_compile_options(-Werror=return-type)                   # error on missing return type
add_compile_options(-Werror=format)                        # error on wrong printf formats
add_compile_options(-Werror=parentheses)                   # error when using ambiguous syntax
include_directories(${PROJECT_SOURCE_DIR}/include)

set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads REQUIRED)


add_executable(main_app
        main.cpp
        src/Processor.cpp
        src/Loader.cpp
        src/Logger.cpp)

Loader.hpp

#pragma once
#include <string>
#include <c-assignment/Processor.hpp>

using namespace std;
class Loader
{
private:
  Processor *Processor_obj; // creating an object out of the Processor class
  std::thread t1;
  Processor boo;


public:
    Loader();
    ~Loader();
    void thr(int time);
    string usr_input;
    void read_usr_input(void);
};

Processor.hpp

#pragma once
#include <string>
#include <thread>

using namespace std;

class Processor
{
public:

    bool status;       //status of processing true = free, false = busy
    float wait_amount; //variable to store the random generated float
    Processor();
    void process(string);
};

Loader.cpp

#include <c-assignment/Loader.hpp>
#include <c-assignment/Logger.hpp>
#include <c-assignment/Processor.hpp>
#include <iostream>
#include <thread>

Loader::Loader()
{
  Processor_obj = new Processor(); // creating an object out of the Processor class
}
Loader::~Loader()
{
  t1.join();
}
void Loader::read_usr_input(void)
{

  std::cout << "Please enter a command" << '\n';
  std::cin >> Loader::usr_input;
  if (Processor_obj->status == true) //check if the Processor is busy or not
  {
    if (Loader::usr_input == "fc" || Loader::usr_input == "out")
    {
      //Processor_obj->process(Loader::usr_input);
      Loader::t1 = std::thread(&Processor::process,Loader::boo,Loader::usr_input);
    }
    //else if (){}
    //else if (){}
    else
    {
    std::cout << "Unknown command" << '\n';
    }
    std::cout << '\n' << "you entered the command" << Loader::usr_input << '\n';
  }
  else {std::cout << "Processor class is busy" << '\n';}
}

Processor.cpp

#include <c-assignment/Processor.hpp>
#include <c-assignment/Logger.hpp>
#include <iostream>
#include <thread>
#include <chrono>
#include <string>
#include <random>
#include <ctime>
using namespace std;

Processor::Processor()
{
  Processor::status = true;
}
void Processor::process(string usr_input)
{
  srand(time(NULL));
  Processor::wait_amount = ((float)rand() / RAND_MAX) * (3.00f - 1.00f) + 1.00f;
  std::cout << "waiting time is" << (Processor::wait_amount)*1000 << "milliseconds" << '\n';
  Processor::status = false;
  std::this_thread::sleep_for(std::chrono::milliseconds((int)(Processor::wait_amount)*1000));
  Processor::status = true;
  std::cout << "/Processed/" << '\n';
}

main.cpp

#include <c-assignment/Processor.hpp>
#include <c-assignment/Loader.hpp>
#include <c-assignment/Logger.hpp>

int main()
{

    while (true) {
        Processor a;
        Loader b;
        Logger c;
        //a.process("rfc");
        b.read_usr_input();

    }
    return 0;
}

这是我运行make时的输出：

    [ 20%] Linking CXX executable main_app
CMakeFiles/main_app.dir/src/Loader.cpp.o: In function `std::thread::thread<void (Processor::*)(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >), Processor&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&>(void (Processor::*&&)(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >), Processor&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&)':
Loader.cpp:(.text._ZNSt6threadC2IM9ProcessorFvNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEEJRS1_RS7_EEEOT_DpOT0_[_ZNSt6threadC5IM9ProcessorFvNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEEJRS1_RS7_EEEOT_DpOT0_]+0xb4): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
CMakeFiles/main_app.dir/build.make:172: recipe for target 'main_app' failed
make[2]: *** [main_app] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/main_app.dir/all' failed
make[1]: *** [CMakeFiles/main_app.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

Answer 1

myList = newMyList输出的重要部分是链接器错误：make。这表明链接器找不到该pthread函数的定义。您还没有链接 CMake中的pthread库，因此您应该尝试这样做以修复错误。在您对undefined reference to 'pthread_create'的CMake调用之后，添加以下行：

add_executable()

这假设您对target_link_libraries(main_app PRIVATE Threads::Threads)的调用正确找到了pthread库并填充了导入的目标Threads::Threads。如果那不起作用，您也可以尝试直接链接到find_package(Threads REQUIRED)库，而不是使用以下内容：

pthread

C ++ CMake项目：目标“ main_app”的配方失败

1 个答案: