UDP编程实例

使用UDP协议通讯时服务器端和客户端无需建立连接，只要知道对方套接字的地址信息，就可以发送数据。服务器端只需创建一个套接字用于接收不同客户端发来的请求，经过处理后再把结果发送给对应的客户端。
服务器端和客户端使用UDP的流程如下图示：

服务器端代码

/*****server.c*****/
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define BUFFER_SIZE 128

int main(int argc, char *argv[]){
    
    
	int sockfd;
	struct sockaddr_in servaddr, cliaddr;
	socklen_t peerlen;
	char[BUFFER_SIZE];

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

	if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1){
    
    		//建立socket连接
		perror("socket");
		exit(-1);
	}
	print("sockfd = %d\n",sockfd);
	
	//设置sockaddr_in结构体中相关参数
	bzero(&servaddr,szieof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(atoi(argv[2]));
	servaddr.sin_addr.s_addr = inet_addr(argv[1]);
	
	if(bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0){
    
    	//bind()绑定地址信息
		perror("bind");
		exit(-1);
	}
	printf("bind success!\n");
	
	peerlen = sizeof(cliaddr);		
	while(1){
    
    		//调用recvfrom()函数接收客户端发送的数据
		if(recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr *)&cliaddr, &peerlen) < 0){
    
    
			perror("recvfrom");
			exit(-1);
		}
		printf("Received a message: %s\n",buf);
		strcpy(buf, "Welcome to server");
		sendto(sockfd, buf, sizeof(buf), 0, (struct sockaddr *)&cliaddr, peerlen);
	}
	
	close(sockfd);
	exit(0);
}

客户端代码

/*****client.c*****/
//头文件同server.c
#define BUFFER_SIZE 128

int main(int argc, char *argv[]){
    
    
	int sockfd;
	char buf[BUFFER_SIZE] = "Hello Server";
	struct sockaddr_in servaddr;

	if(argc < 3){
    
    
		printf("Usage: %s <ip> <port>\n",argv[0]);
		exit(-1);
	}
	
	if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1){
    
    		//创建socket
		perror("socket");
		exit(-1);
	}
	
	//设置sockaddr_in结构体中相关参数
	bzero(&servaddr,szieof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(atoi(argv[2]));
	servaddr.sin_addr.s_addr = inet_addr(argv[1]);

	sendto(sockfd, buf, sizeof(buf), 0, (struct sockaddr *)&servaddr, sizeof(servaddr));	//发送消息给服务器端
	if(recvfrom(sockfd, buf, sizeof(buf), 0, NULL, NULL) < 0){
    
    
		perror("recvfrom");
		exit(-1);
	}
	printf("Recv from server: %s\n",buf);
	close(sockfd);
	exit(0);
}

运行时先启动服务器端，再启动客户端

linux@linux-virtual-machine:~/andy/net$ ./server 192.168.1.100 9999
listenfd = 3
bind success!
Listening...
Received a message: Hello Server
linux@linux-virtual-machine:~/andy/net$ ./client 192.168.1.100 9999
Recv from server: Welcome to server