linux select 使用

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/select.h>

#define MAX_CLIENTS 10
#define BUFFER_SIZE 1024

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int addrlen = sizeof(address);
    char buffer[BUFFER_SIZE] = {0};
    fd_set readfds;

    // 创建 socket
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 绑定 socket
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(8080);
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 监听连接
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    while (1) {
        // 清空文件描述符集合
        FD_ZERO(&readfds);

        // 添加监听的 socket 到集合
        FD_SET(server_fd, &readfds);
        int max_sd = server_fd;

        // 添加已连接的客户端 socket 到集合
        for (int i = 0; i < MAX_CLIENTS; i++) {
            int sd = client_socket[i];
            if (sd > 0) {
                FD_SET(sd, &readfds);
            }
            if (sd > max_sd) {
                max_sd = sd;
            }
        }

        // 使用 select 监听
        int activity = select(max_sd + 1, &readfds, NULL, NULL, NULL);
        if ((activity < 0) && (errno != EINTR)) {
            perror("select error");
        }

        // 检查是否有新的连接
        if (FD_ISSET(server_fd, &readfds)) {
            if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
                perror("accept");
                exit(EXIT_FAILURE);
            }
            printf("New connection, socket fd is %d, ip is: %s, port is: %d\n", new_socket, inet_ntoa(address.sin_addr), ntohs(address.sin_port));
            // 将新连接的 socket 添加到数组中
            for (int i = 0; i < MAX_CLIENTS; i++) {
                if (client_socket[i] == 0) {
                    client_socket[i] = new_socket;
                    break;
                }
            }
        }

        // 检查已连接的客户端是否有数据可读
        for (int i = 0; i < MAX_CLIENTS; i++) {
            int sd = client_socket[i];
            if (FD_ISSET(sd, &readfds)) {
                if ((valread = read(sd, buffer, BUFFER_SIZE)) == 0) {
                    // 客户端断开连接
                    getpeername(sd, (struct sockaddr*)&address, (socklen_t*)&addrlen);
                    printf("Host disconnected, ip %s, port %d\n", inet_ntoa(address.sin_addr), ntohs(address.sin_port));
                    close(sd);
                    client_socket[i] = 0;
                } else {
                    // 处理接收到的数据
                    buffer[valread] = '\0';
                    send(sd, buffer, strlen(buffer), 0);
                }
            }
        }
    }

    return 0;
}