ASIO处理程序参数和boost :: bind，编译时错误

debugcn 发表于 Dev

NRA

我正在努力解决编译时错误，请尝试尝试，但我看不出我是怎么做的错误或与文档/示例中列出的处理程序函数签名不同。（我在Linux上使用Boost 1.41）

请帮助我理解错误！（包括在下面的摘录中）

我的应用程序有一些对象，这些对象的方法是async_ *函数的处理程序。下面是代码片段。在标记为“第58行”的行中报告了错误，我在其中使用了boost :: bind

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

有巨大的错误输出，但相关的行似乎是：

../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）并使用没有参数的处理程序时，它将编译并执行而没有错误。这是修改后的代码段。

    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) {
...
}

看

错误代码不能作为参考。按值或const＆使其：

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

另外，请考虑使用Asio专用占位符：

    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));

也要使用适当的锁止装置。我们在C ++中！使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() {}