C++ 使用boost:：async\u连接问题

我在修补asio的阻塞套接字方面没有任何问题，但我对异步套接字的研究一直是一场噩梦。也许我只是太累了：

  using boost::asio::ip::tcp;

  boost::asio::io_service io_service;

  tcp::resolver resolver(io_service);
  tcp::resolver::query query(newip, newport);
  tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);

  tcp::socket socket(io_service);
  boost::system::error_code ec;

  auto f = std::bind(&Irc::connect_handler, this, boost::asio::placeholders::error,
    boost::asio::placeholders::iterator);
  boost::asio::async_connect(socket, endpoint_iterator, f);

我的处理程序定义为Irc类中的成员函数：

  void connect_handler(
    const boost::system::error_code& ec,
    boost::asio::ip::tcp::resolver::iterator i)
  {
    // ...
  }

我在VS2013上，错误并不漂亮

1>------ Build started: Project: Project18, Configuration: Debug Win32 ------
1>  Irc.cpp
1>c:\program files (x86)\microsoft visual studio 12.0\vc\include\functional(1149): error C2664: 'void std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>>::operator ()(_Farg0 &,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>) const' : cannot convert argument 2 from 'boost::arg<1>' to 'const boost::system::error_code &'
1>          with
1>          [
1>              InternetProtocol=boost::asio::ip::tcp
1>  ,            _Farg0=Irc
1>          ]
1>          Reason: cannot convert from 'boost::arg<1>' to 'const boost::system::error_code'
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\functional(1137) : see reference to function template instantiation 'void std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>>,Irc *const ,boost::arg<1> &,boost::arg<2> &>::_Do_call<Arg1,Arg2,0,1,2>(std::tuple<Arg1 &,Arg2 &>,std::_Arg_idx<0,1,2>)' being compiled
1>          with
1>          [
1>              InternetProtocol=boost::asio::ip::tcp
1>  ,            Arg1=const boost::system::error_code
1>  ,            Arg2=boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\functional(1137) : see reference to function template instantiation 'void std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>>,Irc *const ,boost::arg<1> &,boost::arg<2> &>::_Do_call<Arg1,Arg2,0,1,2>(std::tuple<Arg1 &,Arg2 &>,std::_Arg_idx<0,1,2>)' being compiled
1>          with
1>          [
1>              InternetProtocol=boost::asio::ip::tcp
1>  ,            Arg1=const boost::system::error_code
1>  ,            Arg2=boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>
1>          ]
1>          c:\local\boost_1_55_0\boost\asio\detail\handler_type_requirements.hpp(98) : see reference to function template instantiation 'void std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>>,Irc *const ,boost::arg<1> &,boost::arg<2> &>::operator ()<Arg1&,Arg2&>(Arg1 &,Arg2 &)' being compiled
1>          with
1>          [
1>              InternetProtocol=boost::asio::ip::tcp
1>  ,            Arg1=const boost::system::error_code
1>  ,            Arg2=boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>
1>          ]
1>          c:\local\boost_1_55_0\boost\asio\impl\connect.hpp(257) : see reference to function template instantiation 'void std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>>,Irc *const ,boost::arg<1> &,boost::arg<2> &>::operator ()<Arg1&,Arg2&>(Arg1 &,Arg2 &)' being compiled
1>          with
1>          [
1>              InternetProtocol=boost::asio::ip::tcp
1>  ,            Arg1=const boost::system::error_code
1>  ,            Arg2=boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>
1>          ]
1>          c:\users\c\documents\visual studio 2012\projects\project18\project18\irc.cpp(37) : see reference to function template instantiation 'boost::asio::async_result<Handler>::type boost::asio::async_connect<Protocol,StreamSocketService,boost::asio::ip::basic_resolver_iterator<InternetProtocol>,std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<InternetProtocol>>,Irc *const ,boost::arg<1> &,boost::arg<2> &>&>(boost::asio::basic_socket<Protocol,StreamSocketService> &,Iterator,ComposedConnectHandler)' being compiled
1>          with
1>          [
1>              Handler=std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>>,Irc *const ,boost::arg<1> &,boost::arg<2> &>
1>  ,            Protocol=boost::asio::ip::tcp
1>  ,            StreamSocketService=boost::asio::stream_socket_service<boost::asio::ip::tcp>
1>  ,            InternetProtocol=boost::asio::ip::tcp
1>  ,            Iterator=boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>
1>  ,            ComposedConnectHandler=std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Irc::* )(const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>),void,Irc,const boost::system::error_code &,boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp>>,Irc *const ,boost::arg<1> &,boost::arg<2> &> &
1>          ]
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

1>----构建已启动：项目：项目18，配置：调试Win32------
1> Irc.cpp
1> c:\program files（x86）\microsoft visual studio 12.0\vc\include\functional（1149）：错误C2664:'void std:'u Pmf\u wrap:：operator（）（'u Farg0&，const boost:：system:：error\u code&，boost:：asio:：ip:：basic\u resolver\u iterator）const'：无法将参数2从'boost:：arg'转换为'const boost:：system:：error\u code&'
1> 与
1>          [
1> InternetProtocol=boost:：asio:：ip:：tcp
1> ，_Farg0=Irc
1>          ]
1> 原因：无法从“boost:：arg”转换为“const boost:：system:：error\u code”
1> 没有可执行此转换的用户定义的转换运算符，或者无法调用该运算符
1> c:\ProgramFiles（x86）\microsoft visual studio 12.0\vc\include\functional（1137）：请参阅正在编译的函数模板实例化“void std:：_Bind:：_Do_call（std:：tuple，std:_Arg_idx）”的参考
1> 与
1>          [
1> InternetProtocol=boost:：asio:：ip:：tcp
1> ，Arg1=const boost:：system:：error\u代码
1> ，Arg2=boost:：asio:：ip:：basic\u解析器\u迭代器
1>          ]
1> c:\ProgramFiles（x86）\microsoft visual studio 12.0\vc\include\functional（1137）：请参阅正在编译的函数模板实例化“void std:：_Bind:：_Do_call（std:：tuple，std:_Arg_idx）”的参考
1> 与
1>          [
1> InternetProtocol=boost:：asio:：ip:：tcp
1> ，Arg1=const boost:：system:：error\u代码
1> ，Arg2=boost:：asio:：ip:：basic\u解析器\u迭代器
1>          ]
1> c:\local\boost\u 1\u 55\u 0\boost\asio\detail\handler\u type\u requirements.hpp（98）：请参阅正在编译的函数模板实例化“void std:：\u Bind:：operator（）（Arg1&，Arg2&）”的参考
1> 与
1>          [
1> InternetProtocol=boost:：asio:：ip:：tcp
1> ，Arg1=const boost:：system:：error\u代码
1> ，Arg2=boost:：asio:：ip:：basic\u解析器\u迭代器
1>          ]
1> c:\local\boost\u 1\u 55\u 0\boost\asio\impl\connect.hpp（257）：请参阅正在编译的函数模板实例化“void std:：_Bind:：operator（）（Arg1&，Arg2&）”的参考
1> 与
1>          [
1> InternetProtocol=boost:：asio:：ip:：tcp
1> ，Arg1=const boost:：system:：error\u代码
1> ，Arg2=boost:：asio:：ip:：basic\u解析器\u迭代器
1>          ]
1> c:\users\c\documents\visual studio 2012\projects\project18\project18\irc.cpp（37）：请参阅正在编译的函数模板实例化“boost:：asio:：async\u结果：：type boost:：asio:：async\u connect（boost:：asio:：basic_socket&、迭代器、ComposedConnectHandler）”
1> 与
1>          [
1> Handler=std:：\u绑定
1> ，Protocol=boost:：asio:：ip:：tcp
1> ，StreamSocketService=boost:：asio:：stream\u socket\u服务
1> ，InternetProtocol=boost:：asio:：ip:：tcp
1> ，Iterator=boost:：asio:：ip:：basic\u resolver\u Iterator
1> ，ComposedConnectHandler=std:：\u Bind&
1>          ]
======生成：0成功，1失败，0最新，0跳过==========

您需要将

boost:：bind

与asio占位符一起使用

如果使用

std:：bind

您还需要使用

std:：占位符

。asio占位符仅适用于

boost:：bind

所以这应该可以解决这个问题：

auto f = std::bind(&Irc::connect_handler, this, std::placeholders::_1, std::placeholders::_2);

---

关闭是因为asker已经筋疲力尽了？只需使用lambda而不是bind。早上7点无睡眠编码会导致这种胡说八道，朋友们说实话，我认为使用

boost:：bind

更干净，因为它会让你编写更具表现力的

boost:：asio:：占位符

。另外，

boost:：bind

支持带有成员函数的

boost:：shared_ptr

，这是典型异步服务器位置经常需要的。而且，它的助推作用几乎不成问题：）