linux 错误码 -6

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

int main(int argc, char **argv)
{
    int sockfd;
    int result;
    struct sockaddr_in serv_addr;
    socklen_t length;

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

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

    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);
    }

    // Set socket to non-blocking mode
    int flags = fcntl(sockfd, F_GETFL, 0);
    fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

    result = connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));
    if (result < 0) {
        if (errno == EINPROGRESS) {
            fd_set writefds;
            struct timeval tv;
            tv.tv_sec = 5; // Wait up to 5 seconds
            tv.tv_usec = 0;

            FD_ZERO(&writefds);
            FD_SET(sockfd, &writefds);

            result = select(sockfd + 1, NULL, &writefds, NULL, &tv);
            if (result < 0) {
                perror("select");
                exit(1);
            } else {
                int error = 0;
                socklen_t len = sizeof(error);
                getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &error, &len);
                if (error != 0) {
                    fprintf(stderr, "Connection failed: %s\n", strerror(error));
                    exit(1);
                }
            }
        } else {
            perror("connect");
            exit(1);
        }
    }

    printf("Connected successfully!\n");
    close(sockfd);
    return 0;
}