本文给出一个很实用的C语言实现的服务端和客户端进行TCP通信的小例子。具体实现上非常简单，只是平时编写类似程序，具体步骤经常忘记，还要总是查，暂且将其记下来，方便以后参考。
（1）客户端程序，编写一个文件client.c，内容如下：
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> /* netdb is necessary for struct hostent */
#define PORT 4321 /* server port */
#define MAXDATASIZE 100
int main(int argc, char *argv[])
{
int sockfd, num; /* files descriptors */
char buf[MAXDATASIZE]; /* buf will store received text */
struct hostent *he; /* structure that will get information about remote host */
struct sockaddr_in server;
if (argc != 2)
{
printf("Usage: %s <IP Address>\n",argv[0]);
exit(1);
}
if((he=gethostbyname(argv[1]))==NULL)
{
printf("gethostbyname() error\n");
exit(1);
}
if((sockfd=socket(AF_INET,SOCK_STREAM, 0))==-1)
{
printf("socket() error\n");
exit(1);
}
bzero(&server,sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(PORT);
server.sin_addr = *((struct in_addr *)he->h_addr);
if(connect(sockfd, (struct sockaddr *)&server, sizeof(server))==-1)
{
printf("connect() error\n");
exit(1);
}
char str[] = "horst\n"
if((num=send(sockfd,str,sizeof(str),0))==-1){
printf("send() error\n");
exit(1);
}
if((num=recv(sockfd,buf,MAXDATASIZE,0))==-1)
{
printf("recv() error\n");
exit(1);
}
buf[num-1]='\0';
printf("server message: %s\n",buf);
close(sockfd);
return 0;
}
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（2）服务器端，编写server.c，内容如下
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#include <sys/time.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define PORT 4321
#define BACKLOG 1
#define MAXRECVLEN 1024
int main(int argc, char *argv[])
{
char buf[MAXRECVLEN];
int listenfd, connectfd; /* socket descriptors */
struct sockaddr_in server; /* server's address information */
struct sockaddr_in client; /* client's address information */
socklen_t addrlen;
/* Create TCP socket */
if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
/* handle exception */
perror("socket() error. Failed to initiate a socket");
exit(1);
}
/* set socket option */
int opt = SO_REUSEADDR;
setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
bzero(&server, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(PORT);
server.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(listenfd, (struct sockaddr *)&server, sizeof(server)) == -1)
{
/* handle exception */
perror("Bind() error.");
exit(1);
}
if(listen(listenfd, BACKLOG) == -1)
{
perror("listen() error. \n");
exit(1);
}
addrlen = sizeof(client);
while(1){
if((connectfd=accept(listenfd,(struct sockaddr *)&client, &addrlen))==-1)
{
perror("accept() error. \n");
exit(1);
}