#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>

int main(int argc, char *argv[])
{
        int fd;
        struct sockaddr_in addr;
        struct timeval timeo = {3, 0};
        socklen_t len = sizeof(timeo);

        fd = socket(af_inet, sock_stream, 0);
        if (argc == 4)(来源 www.iocblog.net)
                timeo.tv_sec = atoi(argv[3]);
        setsockopt(fd, sol_socket, so_sndtimeo, &timeo, len);
        addr.sin_family = af_inet;
        addr.sin_addr.s_addr = inet_addr(argv[1]);
        addr.sin_port = htons(atoi(argv[2]));
        if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
                if (errno == einprogress) {
                        fprintf(stderr, "timeout ");
                        return -1;
                }
                perror("connect");
                return 0;
        }
        printf("connected ");

        return 0;
}