[英]boost::asio::async_read_until problem
我正在嘗試從 boost asio 修改回顯服務器示例,當我嘗試使用 boost::asio::async_read_until 時遇到了問題。 這是代碼:
#include <cstdlib>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
class session
{
public:
session(boost::asio::io_service& io_service)
: socket_(io_service)
{
}
tcp::socket& socket()
{
return socket_;
}
void start()
{
std::cout<<"starting"<<std::endl;
boost::asio::async_read_until(socket_, boost::asio::buffer(data_, max_length), ' ',
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
void handle_read(const boost::system::error_code& error,
size_t bytes_transferred)
{
std::cout<<"handling read"<<std::endl;
if (!error)
{
boost::asio::async_write(socket_,
boost::asio::buffer(data_, bytes_transferred),
boost::bind(&session::handle_write, this,
boost::asio::placeholders::error));
}
else
{
delete this;
}
}
void handle_write(const boost::system::error_code& error)
{
if (!error)
{
/*
socket_.async_read_some(boost::asio::buffer(data_, max_length),
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
*/ }
else
{
delete this;
}
}
private:
tcp::socket socket_;
enum { max_length = 1024 };
char data_[max_length];
};
class server
{
public:
server(boost::asio::io_service& io_service, short port)
: io_service_(io_service),
acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
{
session* new_session = new session(io_service_);
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
void handle_accept(session* new_session,
const boost::system::error_code& error)
{
if (!error)
{
new_session->start();
new_session = new session(io_service_);
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
else
{
delete new_session;
}
}
private:
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
};
int main(int argc, char* argv[])
{
try
{
if (argc != 2)
{
std::cerr << "Usage: async_tcp_echo_server <port>\n";
return 1;
}
boost::asio::io_service io_service;
using namespace std; // For atoi.
server s(io_service, atoi(argv[1]));
io_service.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
問題是當我嘗試編譯時出現這個奇怪的錯誤:
server.cpp:在成員函數“void session::start()”中:server.cpp:27:錯誤:沒有匹配的函數調用“async_read_until(boost::asio::basic_stream_socket >&, boost::asio:: mutable_buffers_1, char, boost::_bi::bind_t, boost::_bi::list3, boost::arg<1> ( )(), boost::arg<2> ( )()> >)'
有人可以解釋一下發生了什么嗎? 據我所知, async_read_until 的參數是正確的。
謝謝!
async_read_until 的第二個參數應該是一個streambuf 對象,數據將被讀取到該對象中。 簡單來說,您需要通過引用傳遞boost::asio::streambuf
,而不是通過值傳遞boost::asio::buffer
。
無需使用streambufs
。 有接受動態緩沖區的重載。 動態是關鍵,因為read_until
意味着需要一個可以由被調用者自行決定增加其大小的緩沖區。 因此,您所需要的只是用boost::asio::dynamic_buffer
替換對boost::asio::buffer
調用,並在std::string
或std::vector<char>
上調用它。
...
void start()
{
std::cout<<"starting"<<std::endl;
boost::asio::async_read_until(
socket_, boost::asio::dynamic_buffer(data_), ' ',
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
...
private:
tcp::socket socket_;
std::string data_;
// or
//std::vector<char> data_;
};
我也會擺脫boost::bind
因為它是一種矯枉過正並使用 lambda (盡可能多地使用它們)
[this](const boost::system::error_code& error, size_t bytes_transferred) {
handle_read(error, bytes_transferred);
}
const (in) 正確性也可能導致此類錯誤消息。
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