C++判断端口号占用

在C++中，可以通过以下方式判断端口号是否被占用：

1. 引入头文件：

#include <winsock2.h>
#include <ws2tcpip.h>

2. 创建一个socket：

SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

3. 设置socket选项：

int optval = 1;
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char*)&optval, sizeof(optval));

这里设置了SO_REUSEADDR选项，表示可以重用本地地址和端口。

4. 绑定socket到指定的IP地址和端口号：

sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_port = htons(port);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
bind(sock, (sockaddr*)&addr, sizeof(addr));

如果端口号已被占用，则bind函数会失败，并返回SOCKET_ERROR。

完整的代码如下：

#include <winsock2.h>
#include <ws2tcpip.h>
#include <iostream>

#pragma comment(lib, "ws2_32.lib")

int main() {
    int port = 8080;

    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
        std::cerr << "WSAStartup failed\n";
        return 1;
    }

    SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock == INVALID_SOCKET) {
        std::cerr << "socket failed\n";
        return 1;
    }

    int optval = 1;
    if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char*)&optval, sizeof(optval)) == SOCKET_ERROR) {
        std::cerr << "setsockopt failed\n";
        return 1;
    }

    sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    addr.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(sock, (sockaddr*)&addr, sizeof(addr)) == SOCKET_ERROR) {
        std::cerr << "bind failed\n";
        return 1;
    }

    std::cout << "port " << port << " is available\n";

    closesocket(sock);
    WSACleanup();

    return 0;
}

如果端口号未被占用，则输出“port 8080 is available”。如果端口号已被占用，则输出“bind failed”。