如何获取错误对象？在deadline_timer中使用成员函数时

Posted 2023-02-22

【中文标题】如何获取错误对象？在deadline_timer中使用成员函数时

【英文标题】：How to get error object? when use member function in deadline_timer

【发布时间】：2014-10-23 06:43:28

【问题描述】：

我使用 boost::asio::deadline_timer 使用成员函数作为处理程序（回调函数）。

如果我取消定时器，如何在 print() 成员函数中获取错误对象？

class printer

public:
    printer(boost::asio::io_service& io)
        : timer_(io, boost::posix_time::seconds(1)),
          count_(0)
    
        timer_.async_wait(boost::bind(&printer::print, this));
    
    ~printer()
    
        std::cout << "Final count is " << count_ << "\n";
    
    void print()
    
        if (count_ < 5)
        
            std::cout << count_ << "\n";
            ++count_;

            timer_.expires_at(timer_.expires_at() + boost::posix_time::seconds(1));
            timer_.async_wait(boost::bind(&printer::print, this));
        
    

private:
    boost::asio::deadline_timer timer_;
    int count_;
;

int main()

    boost::asio::io_service io;
    printer p(io);
    io.run();

    return 0;

我尝试在 async_wait() 中使用 bind 设置错误对象，但编译错误

timer_.async_wait(boost::bind(&printer::print, this, boost::asio::placeholders::error));

【问题讨论】：

您没有提供编译器错误消息。这很奇怪，因为您对此有疑问。

@sehe 谢谢 :) 我写了一个错误的成员函数签名，比如 void print(boost::system::error_code ec)。 const 关键字被省略。而且，我下次必须写错误信息。

【参考方案1】：

只要你的方法签名匹配，应该没问题：

void print(boost::system::error_code const ec)

// and

boost::bind(&printer::print, this, boost::asio::placeholders::error)

看到它Live On Coliru：

#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <iostream>

class printer

public:
    printer(boost::asio::io_service& io)
        : timer_(io, boost::posix_time::seconds(1)),
          count_(0)
    
        timer_.async_wait(boost::bind(&printer::print, this, boost::asio::placeholders::error));
    
    ~printer()
    
        std::cout << "Final count is " << count_ << "\n";
    

    void print(boost::system::error_code const ec)
    
        if (ec)
            std::cout << "Error: " << ec.message() << "\n";
        if (count_ < 5)
        
            std::cout << count_ << "\n";
            ++count_;

            timer_.expires_at(timer_.expires_at() + boost::posix_time::seconds(1));
            timer_.async_wait(boost::bind(&printer::print, this, boost::asio::placeholders::error));
        
    

private:
    boost::asio::deadline_timer timer_;
    int count_;
;

int main()

    boost::asio::io_service io;
    printer p(io);
    io.run();