boost :: asio :: ip :: tcp :: iostream，首先启动客户端并等待服务器？

Posted 2021-05-06

我有一个应用程序，它使用boost :: asio :: ip :: tcp :: iostream通过tcp连接到另一个应用程序。

我的服务器代码是：

static auto const flags = boost::archive::no_header | boost::archive::no_tracking;
boost::asio::io_service ios;
boost::asio::ip::tcp::endpoint endpoint
= boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), 4444);
boost::asio::ip::tcp::acceptor acceptor(ios, endpoint);
boost::asio::ip::tcp::iostream stream;

//program stops here until client connects.
acceptor.accept(*stream.rdbuf());

我的客户是：

std::string ip = "127.0.0.1";

    boost::asio::ip::tcp::iostream stream(ip, "4444");

    if (!stream)
        throw std::runtime_error("can't connect");

如果首先启动服务器，这很有用。但是如果首先启动客户端，它将抛出错误并崩溃。我想做的是能够先启动任何一方，然后让它等待连接。客户显然是问题，所以我想：

 bool bConnected;

    std::string ip = "127.0.0.1";
    boost::asio::ip::tcp::iostream* stream;

    while (!bConnected)
    {
        stream = new boost::asio::ip::tcp::iostream(ip, "4444");
        if (!stream)
        {
            std::cout << "cannot find datastream" << std::endl;
            std::this_thread::sleep_for(std::chrono::milliseconds(50));
            //throw std::runtime_error("can't connect");
        }

        if (stream)
        {
            bConnected = true;
        }

    }

这将无法编译，使用boost::asio::ip::tcp::iostream* stream给Error C4703 potentially uninitialized local pointer variable 'stream' used一个错误。我试过了：

boost::asio::ip::tcp::iostream* stream = nullptr; boost::asio::ip::tcp::iostream* stream = NULL;

既编译，又崩溃。在这种情况下，如何让客户端等待服务器？

答案

切勿使用new¹。因为正如你评论的那样，if (!*stream)编译但它泄漏了资源，就像没有明天一样。

在这种情况下：

Live On Coliru

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

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

int main() {
    tcp::iostream stream;

    do {
        std::cout << "Connecting...
";

        stream.clear();
        stream.connect("127.0.0.1", "4444");

        std::this_thread::sleep_for(std::chrono::milliseconds(500));
    } while (!stream);

    std::cout << "Connected! " << stream.rdbuf();
}

哪个印刷品：

Connecting...
Connecting...
Connecting...
Connecting...
Connecting...
Connecting...
Connected! Hello world

---

¹除非您正在为库接口编写低级资源包装器。