TCP通信的过程为：

一. 服务器端：

   1.socket(int domain,int type,int protocol):建立套接字；

   2 .bind(int sockid,struct sockaddr *addrp,socklen_t addrlen):绑定端口和地址信息；

   3.listen(int sockid,int qsize):监听套接字;

   4.fd=accept(int sockid,struct sockaddr *callerid,socklen_t *addrlenp):等待套接字；

   5.recv(int fd,void *buf,size_t nbytes,int flags):从套接字接收数据;

   6.close(fd) 和close(sockid) 关闭套接字

  二.客户端：

   1. socket():建立套接字；

   2.connect(int sockid,struct sockaddr *serv_addrp,socklen_t addrlen):连接到服务器；

   3. send(int sockfd,const void *buf,size_t nbytes,int flags):发送数据到服务器.

   4. close(sockid);关闭套接字

TCP通信服务器端程序：

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

# define MAX_SIZE 256
int main()
{
int err;
int listenfd,connfd;
struct sockaddr_in servaddr,clientaddr;
int n,addrlen=sizeof(struct sockaddr_in);
char addr[16];
char rbuf[MAX_SIZE];
char sbuf[MAX_SIZE]="hello from server";
inet_pton(AF_INET,"127.0.0.1",&servaddr.sin_addr);
memset(&servaddr,0,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_port=htons(10000);
listenfd=socket(AF_INET,SOCK_STREAM,0);
if(listenfd==-1)
{
perror("socket");
return -1;
}
err=bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr));
if(err==-1)
{
perror("bind");
return -1;
}
err=listen(listenfd,20);
if(err==-1)
{
perror("listen");
return -1;
}
while(1)
{
connfd=accept(listenfd,(struct sockaddr*)&clientaddr,(socklen_t*)&addrlen);
break;
}
n=recv(connfd,rbuf,MAX_SIZE,0);
if(n==-1)
{
perror("recv");
return -1;
}
rbuf[n]='\0';
printf("%s\n",rbuf);
n=send(connfd,sbuf,strlen(sbuf)+1,0);
if(n==-1)
{
perror("send");
return -1;
}
close(connfd);
close(listenfd);
return 0;
}

客户端程序：

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

# define MAX_SIZE 256
int main()
{
int err;
int sockfd,n;
char rbuf[MAX_SIZE],sbuf[MAX_SIZE]="hello from client";
struct sockaddr_in  servaddr;
memset(&servaddr,0,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_port=htons(10000);
inet_pton(AF_INET,"127.0.0.1",&servaddr.sin_addr);
sockfd=socket(AF_INET,SOCK_STREAM,0);
if(sockfd==-1)
{
perror("socket");
return -1;
}
err=connect(sockfd,(struct sockaddr*)&servaddr,(socklen_t)sizeof(servaddr));
if(err<0)
{
perror("connect");
return -1;
}
n=send(sockfd,sbuf,strlen(sbuf)+1,0);
if(n<0)
{
perror("send");
return -1;
}
n=recv(sockfd,rbuf,MAX_SIZE,0);
if(n<0)
{
perror("recv");
return -1;
}
rbuf[n]='\0';
printf("%s\n",rbuf);
close(sockfd);
return 0;
}