[!Tip]

看了套接字编程，先自己实现，出错了或者哪一步没头绪了，再来看这个文档。不要一上来，就无脑抄。

本实例旨在实现简单的echo服务，客户端发送数据给服务端，在服务端打印出来并且回发给客户端，并在客户端显示。

1. TCP服务端

TCPserver.c

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

#define BACKLOG 10
#define BUFFER_SIZE 1024

int main(int argc, char *argv[])
{
  if(2 != argc)
  {
    printf("Usage:%s portnumber\n", argv[0]);
    return - 1;
  }

  /***1.create a socket***/
  int fd_server = socket(AF_INET, SOCK_STREAM, 0); //TCP
  if( - 1 == fd_server)
  {
    printf("%s\n", strerror(errno));
    return - 1;
  }

  /***2.bind the socket***/
  int listen_port = atoi(argv[1]);
  struct sockaddr_in addr_server;
  //memset(&addr_server, 0, sizeof(addr_server));
  addr_server.sin_family = AF_INET;
  addr_server.sin_port = htons(listen_port);
  addr_server.sin_addr.s_addr = htonl(INADDR_ANY);

  if(bind(fd_server, (struct sockaddr*) &addr_server, sizeof(addr_server)) == - 1)
  {
    printf("%s\n", strerror(errno));
    return - 1;
  }

  /***3.listen the socket***/
  if(listen(fd_server, BACKLOG) == - 1)
  {
    printf("%s\n", strerror(errno));
    return - 1;
  }

  /***4.accept the requirement of some client***/
  struct sockaddr_in addr_client;
  int len_addr_client = sizeof(addr_client);
  int fd_client = accept(fd_server, (struct sockaddr*) &addr_client, &len_addr_client);
  if( - 1 == fd_client)
  {
    printf("%s\n", strerror(errno));
    return - 1;
  }

  /****5.serve the client******/
  char buf[BUFFER_SIZE];
  int size;
  while(1)
  {
    /***read from client***/
    size = recv(fd_client, buf, sizeof(buf), 0);
    buf[size] = '\0';
    printf("%s\n", buf);

    /***write to client***/
    size = send(fd_client, buf, strlen(buf), 0);
  }

  /****6.close the socket******/
  close(fd_server);
  close(fd_client);
}

2. TCP客户端

TCPclient.c

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

#define BUFFER_SIZE 1024

int main(int argc, char *argv[])
{
  if(3 != argc)
  {
    printf("Usage:%s hostname portnumber\n", argv[0]);
    return - 1;
  }

  /***1.create a socket***/
  int fd_client = socket(AF_INET, SOCK_STREAM, 0); //TCP
  if( - 1 == fd_client)
  {
    printf("%s\n", strerror(errno));
    return - 1;
  }
  /***2.connect to the server***/
  int portnumber = atoi(argv[2]);
  struct sockaddr_in addr_server;
  addr_server.sin_family = AF_INET;
  addr_server.sin_port = htons(portnumber);
  if(0 == inet_pton(AF_INET, argv[1], (void*) &addr_server.sin_addr.s_addr))
  {
    printf("Invalid address.\n");
    return - 1;
  }

  if(connect(fd_client, (struct sockaddr*) &addr_server, sizeof(addr_server)) == - 1)
  {
    printf("%s\n", strerror(errno));
    return - 1;
  }


  /****3.get the server******/
  char buf[BUFFER_SIZE];
  int size;
  while(1)
  {
    /***write to server***/
    scanf("%s", buf);
    size = send(fd_client, buf, strlen(buf), 0);

    /***read from server***/
    size = recv(fd_client, buf, BUFFER_SIZE, 0);

    buf[size] = '\0';
    printf("%s\n", buf);

  }
  /****4.close the socket******/
  close(fd_client);
}

2.3 测试结果

运行服务端程序./TCPserver 2000：

运行客户端程序./TCPclient 127.0.0.1 2000：