ASIO处理程序参数和boost :: bind，编译时错误

Question

我在编译时错误，努力尝试，因为我可能，我没有看到以什么方式做错了或不同于处理函数签名文档/例子。 （我在Linux上使用Boost 1.41）

请帮我理解错误！ （包含在下面作为片段）

我的应用程序具有对象，其方法是用于async_ *函数的处理程序。以下是代码片段。报道中标记为“第58行”，在这里我使用boost ::绑定行的错误

class RPC { 

public: 
    char recv_buffer[56]; 

    void data_recv (void) { 
     socket.async_read_some (
       boost::asio::buffer(recv_buffer), 
       boost::bind (&RPC::on_data_recv, this, _1, _2) 
     ); // **<<==== this is line 58, that shows up in error listing** 

     global_stream_lock.lock(); 
     std::cout << "[" << boost::this_thread::get_id() 
      << "] data recvd" << std::endl; 
     global_stream_lock.unlock(); 

    } // RPC::data_recv 

    void on_data_recv (boost::system::error_code& ec, std::size_t bytesRx) { 
     global_stream_lock.lock(); 
     std::cout << "[" << boost::this_thread::get_id() 
      << "] bytes rcvd: " << std::endl; 
     global_stream_lock.unlock(); 

     data_recv(); // call function that waits for more data 

    } // RPC::on_data_recv 

}; // RPC class def 

有一个巨大的错误输出，但相关的线似乎是：

../src/besw.cpp:58: instantiated from here 
/usr/include/boost/bind/bind.hpp:385: error: no match for call to ‘(boost::_m fi::mf2<void, RPC, boost::system::error_code&, long unsigned int>) (RPC*&, boost::asio::error::basic_errors&, int&)’ 
/usr/include/boost/bind/mem_fn_template.hpp:272: note: candidates are: R boost::_mfi::mf2<R, T, A1, A2>::operator()(T*, A1, A2) const [with R = void, T = RPC, A1 = boost::system::error_code&, A2 = long unsigned int] 
/usr/include/boost/bind/mem_fn_template.hpp:291: note:    R boost::_mfi::mf2<R, T, A1, A2>::operator()(T&, A1, A2) const [with R = void, T = RPC, A1 = boost::system::error_code&, A2 = long unsigned int] 
make: *** [src/besw.o] Error 1 

当我删除占位符（_1和_2）并且没有参数的处理程序时，它会编译并执行而不会出错。这是修改后的代码片段。

void data_recv (void) { 
    socket.async_read_some (
      boost::asio::buffer(recv_buffer), 
      boost::bind (&RPC::on_data_recv, this) 
    ); 

    global_stream_lock.lock(); 
    std::cout << "[" << boost::this_thread::get_id() 
     << "] data recvd" << std::endl; 
    global_stream_lock.unlock(); 

} // RPC::data_recv 

void on_data_recv (void) { 
... 
} 

Answer 1

错误代码不能被引用。按值或常量&使其：

void on_data_recv(boost::system::error_code/* ec */, size_t /*bytes_transferred*/) { 

而且，考虑使用短耳特定的占位符：

socket.async_read_some(boost::asio::buffer(recv_buffer), 
          boost::bind(&RPC::on_data_recv, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)); 

还可以使用适当的锁定后卫。我们使用C++！让事情变得异常安全很容易，为什么不呢？

Live On Coliru

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

#include <boost/thread.hpp> 

static boost::mutex global_stream_lock; 

class RPC { 
    char recv_buffer[56]; 
    public: 

    void data_recv() { 
     socket.async_read_some(boost::asio::buffer(recv_buffer), 
           boost::bind(&RPC::on_data_recv, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)); 

     boost::lock_guard<boost::mutex> lk(global_stream_lock); 
     std::cout << "[" << boost::this_thread::get_id() << "] data recvd" << std::endl; 
     global_stream_lock.unlock(); 
    } 

    void on_data_recv(boost::system::error_code/* ec */, size_t /*bytes_transferred*/) { 
     { 
      boost::lock_guard<boost::mutex> lk(global_stream_lock); 
      std::cout << "[" << boost::this_thread::get_id() << "] bytes rcvd: " << std::endl; 
     } 

     data_recv(); // call function that waits for more data 
    } 

    boost::asio::io_service service; 
    boost::asio::ip::tcp::socket socket{service}; 
}; // RPC class def 

int main() {}