select函数demo

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>

#define MAX_SELECT_CLIENT 4096

int select_demo() {

    //建立socket
    int fd = socket(AF_INET, SOCK_STREAM, 0);

    //打开端口复用
    int reuse_port = 1;
    setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &reuse_port, sizeof(int));

    //绑定地址
    struct sockaddr_in bind_address;
    memset(&bind_address, 0, sizeof(struct sockaddr_in));
    bind_address.sin_addr.s_addr = inet_addr("0.0.0.0");
    bind_address.sin_family = AF_INET;
    bind_address.sin_port = htons(8088);
    int code = bind(fd, (struct sockaddr *) &bind_address, sizeof(struct sockaddr_in));
    if (code == -1) {
        perror("bind error");
        close(fd);
        return -1;
    }
    //设置监听状态
    code = listen(fd, 1024);
    if (code == -1) {
        perror("listen error");
        close(fd);
        return -1;
    }

    //定义可读描述符集合
    fd_set read_fd_set;
    FD_ZERO(&read_fd_set);
    FD_SET(fd, &read_fd_set);

    int fd_arr[MAX_SELECT_CLIENT];
    for (int i = 0; i < MAX_SELECT_CLIENT; ++i) {
        fd_arr[i] = -1;
    }
    int max_index = -1;

    int max_fd = fd;
    while (1) {
        FD_ZERO(&read_fd_set);
        FD_SET(fd, &read_fd_set);
        for (int i = 0; i <= max_index; ++i) {
            if (fd_arr[i] == -1) {
                continue;
            }
            FD_SET(fd_arr[i], &read_fd_set);
            if (fd_arr[i] > max_fd) {
                max_fd = fd_arr[i];
            }
        }
        code = select(max_fd + 1, &read_fd_set, NULL, NULL, NULL);
        if (code < 0) {
            perror("select error");
            break;
        } else if (code == 0) {
            continue;
        } else {
            //监听到变化
            if (FD_ISSET(fd, &read_fd_set)) {
                // accept
                printf("acceptn");
                int new_fd = accept(fd, NULL, NULL);
                if (new_fd == -1) {
                    perror("accept error");
                } else {
                    int use_index = -1;
                    for (int i = 0; i < MAX_SELECT_CLIENT; ++i) {
                        if (fd_arr[i] == -1) {
                            fd_arr[i] = new_fd;
                            use_index = i;
                            break;
                        }
                    }
                    if (use_index == -1) {
                        printf("客户端连接过多...n");
                        continue;
                    }
                    if (use_index > max_index) {
                        max_index = use_index;
                    }
                }
            } else {
                for (int i = 0; i <= max_index; ++i) {
                    int cfd = fd_arr[i];
                    if (FD_ISSET(cfd, &read_fd_set)) {
                        char buf[1024] = "";
                        ssize_t return_num = read(cfd, buf, 1024);
                        if (return_num == -1) {
                            perror("read error");
                            close(cfd);
                            fd_arr[i] = -1;
                        } else if (return_num == 0) {
                            printf("closen");
                            close(cfd);
                            fd_arr[i] = -1;
                        } else {
                            printf("receive:%sn", buf);
                            write(cfd, buf, return_num);
                        }
                    }
                }
            }
        }
    }
    return 1;
}

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