echo_client2.c

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

#define BUF_SIZE 1024
void error_handling(char *message);

int main(int argc, char *argv[])
{
    int sock;
    char message[BUF_SIZE];
    int str_len,recv_len,recv_cnt;
    struct sockaddr_in serv_adr;

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

    sock = socket(PF_INET, SOCK_STREAM, 0);
    if (sock == -1)
        error_handling("socket() error");

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_adr.sin_port = htons(atoi(argv[2]));

    // 若调用该函数引起的连接请求被注册到服务器端等待队列，则connect函数将完成正常调用
    if (connect(sock, (struct sockaddr *)&serv_adr, sizeof(serv_adr)) == -1)
        error_handling("connect() error!");
    else
        puts("Connected...........");

    while (1)
    {
        fputs("Input message(Q to quit): ", stdout);
        fgets(message, BUF_SIZE, stdin);

        if (!strcmp(message, "q\n") || !strcmp(message, "Q\n"))
            break;

        str_len = write(sock, message, strlen(message));

        recv_len = 0;
        while(recv_len < str_len)
        {
            recv_cnt = read(sock,&message[recv_len],BUF_SIZE-1);
            if(recv_cnt==-1)
                error_handling("read() error!");
            recv_len+=recv_cnt;
        }
        message[str_len] = 0;
        printf("Message from server: %s", message);
    }
    close(sock); //调用close向相应套接字发送EOF(EOF意味着连接中断)
    return 0;
}

void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}