linux select 机制

#include <sys/select.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char **argv)
{
    int result;
    int fd;
    int n;
    socklen_t length;

    if (argc != 3) {
        fprintf(stderr, "Usage: %s<ip> <port>\n", argv[0]);
        exit(1);
    }

    fd = socket(AF_INET, SOCK_STREAM, 0);
    if (fd < 0) {
        perror("socket");
        exit(1);
    }

    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(atoi(argv[2]));

    if (inet_pton(AF_INET, argv[1], &serv_addr.sin_addr) <= 0) {
        perror("inet_pton");
        exit(1);
    }

    result = connect(fd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));
    if (result < 0) {
        perror("connect");
        exit(1);
    }

    fd_set readfds, writefds, exceptfds;
    struct timeval timeout;

    timeout.tv_sec = 5; // 设置超时时间
    timeout.tv_usec = 0;

    timeout.tv_sec = 5;
    timeout.tv_usec = 0;
    result = select(fd + 1, &readfds, &writefds, &exceptfds, &timeout);
    if (result < 0) {
        perror("select");
        exit(1);
    } else {
        if (FD_ISSET(fd, &readfds)) {
            char buf[1024];
            ssize_t n = read(fd, buf, sizeof(buf));
            if (n < 0) {
                perror("read");
                exit(1);
            }
            printf("Received data: %s\n", buf);
        } else if (FD_ISSET(fd, &writefds)) {
            printf("Socket is writable\n");
        } else if (FD_ISSET(fd, &exceptfds)) {
            printf("Socket error occurred\n");
        }
    }

    close(fd);
    return 0;
}