Boost C++回调返回数据的语法问题求助

我在实现Boost C++回调时，需要从回调中获取返回数据（向回调传递参数），但遇到了语法问题。当前无返回值的回调可以正常触发，但切换为代码中注释的带参数写法后无法正常工作，求指导。

无返回值时的输出：

j1 : 1
j2 : 1
j1 : 2
j2 : 2
j1 : 3
acceptResult
j1 : 4
acceptResult

问题原因与解决步骤 #

核心问题是绑定回调时未为参数预留占位符，导致函数签名不匹配。需要修改以下几个关键点：

• 启用带参数的callback类型定义
• 调整A::acceptResult为带参数的函数
• 在B类中调用回调时传入参数
• 使用Boost Bind的占位符_1匹配回调的参数

修改后的完整代码 #

#include <iostream>
#include <boost/bind.hpp>
#include <boost/thread.hpp>
#include <boost/asio.hpp>
#include <map>
#include <string>

//typedef boost::function<void()> callback;       
typedef boost::function<void(std::string)> callback;    // 启用带参数的回调类型

class B
{
public:
    B(boost::asio::io_service& io, std::string name_, int target_, callback call_)
    : timer_(io, boost::posix_time::seconds(1)),
      count(1), target(target_), name(name_), call(call_)
    {
        timer_.async_wait(boost::bind(&B::print, this));
    }
    
    ~B()
    {
        std::cout << "Final count is " << count << "\n";
    }
 
    void print()
    {
        if (count < target)
        {
            std::cout << name << " : " << count << "\n";
            ++count;

            timer_.expires_at(timer_.expires_at() + boost::posix_time::seconds(1));
            timer_.async_wait(boost::bind(&B::print, this));
        } 
        else {
            //call();
            call(name); // 调用回调时传入job名称参数
        }
    }

private:
    callback call;
    boost::asio::deadline_timer timer_;
    int count;
    int target;
    std::string name;
};

class A {
private:
    std::map<std::string, B*> jobs;
    boost::asio::io_service io;

public:
    //void acceptResult()
    void acceptResult(std::string jobID_) // 修改为带参数的函数
    {
        //std::cout << "acceptResult" << std::endl; 
        std::cout << "acceptResult from job : " << jobID_<< std::endl; 
        // 释放对应job资源
        delete jobs.at(jobID_);   
        auto it = jobs.find(jobID_);
        jobs.erase(it);
    }

    void newJob(std::string jobID_, unsigned int target)
    {
        // 使用_1占位符，为回调的参数预留位置
        B *b = new B(io, jobID_, target, boost::bind(&A::acceptResult, this, _1));
        jobs.insert({jobID_, b});
    }

    void run()
    {
        io.run();
    }
};

int main()
{
    A a;
    a.newJob("j1", 5);
    a.newJob("j2", 3);

    a.run();

    return 0;
}

修改后的输出示例 #

j1 : 1
j2 : 1
j1 : 2
j2 : 2
j1 : 3
acceptResult from job : j2
Final count is 3
j1 : 4
acceptResult from job : j1
Final count is 5

内容的提问来源于stack exchange，提问作者Paul