Question

我正在尝试使用C ++学习网络，并且试图建立一个简单的演示，在该示例中，我在端口5000上打开一个TCP服务器，然后立即将其关闭。这是我的代码：

#include <iostream>
#include <sys/socket.h>
#include <netinet/in.h>

int main()
{
    int port = 5000;
    std::cout << "Port: " << port << "\n";
    int socketdesc = socket(SOCK_STREAM, AF_INET, 0);

    if (socketdesc == 0)
    {
        std::cout << "Failed to create socket description.\n";
        return 1;
    }

    int opt = 1;

    if (setsockopt(socketdesc, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
               &opt, sizeof(opt)))
    {
        std::cout << "Failed to attach socket.\n";
        return 1;
    }

    struct sockaddr_in address;
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(port);

    if (bind(socketdesc, (struct sockaddr *)&address,
         sizeof(address)) < 0)
    {
        std::cout << "Failed to bind socket!\n";
        return 1;
    }

    std::cout << "Listening with protocol TCP on port" << port << ".\n";

    if (listen(socketdesc, 3) < 0)
    {
        std::cout << "Failed to listen!\n";
        return 1;
    }

    if (shutdown(socketdesc, SHUT_RDWR) < 0)
    {
        std::cout << "Failed to close socket!\n";
        return 1;
    }

    std::cout << "TCP test succeeeded.\n";
    return 0;
}

尝试将套接字绑定到端口5000时出现错误。设置TCP服务器端口出了什么问题？

P.S：opt位到底是什么（我正在关注一个教程，同时查看sys / socket的文档）？

Answer 1

在您到达bind()之前，您的代码中存在一些错误：

int socketdesc = socket（SOCK_STREAM，AF_INET，0）;

您将前两个参数值向后移动，则调用应改为如下所示：

int socketdesc = socket(AF_INET, SOCK_STREAM, 0);

如果（socketdesc == 0）

socket()在错误时返回-1，而不是0。

如果（setsockopt（socketdesc，SOL_SOCKET，SO_REUSEADDR | SO_REUSEPORT，＆opt，sizeof（opt）））

setsockopt()也会在错误时返回-1。

但更重要的是，您不能像这样在单个调用中组合多个套接字选项。您需要分别为每个选项调用setsockopt()：

if (setsockopt(socketdesc, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0)
...

if (setsockopt(socketdesc, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt)) < 0)
...

话虽如此，请尝试以下操作：

#include <iostream>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main()
{
    int port = 5000;
    std::cout << "Port: " << port << "\n";

    int socketdesc = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (socketdesc == -1)
    {
        std::cout << "Failed to create socket descriptor. " << strerror(errno) << "\n";
        return 1;
    }

    int opt = 1;

    if (setsockopt(socketdesc, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0)
    {
        std::cout << "Failed to set SO_REUSEADDR option. " << strerror(errno) << "\n";
        return 1;
    }

    if (setsockopt(socketdesc, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt)) < 0)
    {
        std::cout << "Failed to set SO_REUSEPORT option. " << strerror(errno) << "\n";
        return 1;
    }

    struct sockaddr_in address;
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(port);

    if (bind(socketdesc, (struct sockaddr *)&address, sizeof(address)) < 0)
    {
        std::cout << "Failed to bind socket! " << strerror(errno) << "\n";
        return 1;
    }

    std::cout << "Listening with protocol TCP on port" << port << ".\n";

    if (listen(socketdesc, 3) < 0)
    {
        std::cout << "Failed to listen on socket! " << strerror(errno) << "\n";
        return 1;
    }

    if (shutdown(socketdesc, SHUT_RDWR) < 0)
    {
        std::cout << "Failed to close socket! " << strerror(errno) << "\n";
        return 1;
    }

    close(socketdesc);

    std::cout << "TCP test succeeeded.\n";
    return 0;
}

Answer 2

即使现在不是这种情况，我将在此处保留此答案。我认为这仍然是一个真实的案例，有人在网站上寻找答案可能会对此表示赞赏。

（上面代码的真正答案是在注释中）

您需要关闭套接字，但尚未在每个故障状态下都关闭。即使过程结束，它也会保持打开状态并阻止您再次绑定它。

如果不是这种情况，则可能有其他程序在使用该端口。尝试更改端口号。

C ++-bind（）失败

2 个答案: