udpser.c

这个是linux下

	#include <stdio.h>          /* These are the usual header files */ 
        //#include <strings.h>          /* for bzero() */
	#include <string.h> 
	#include <unistd.h>         /* for close() */
	#include <sys/types.h> 
	#include <sys/socket.h>
	#include <stdlib.h> 
	#include <netinet/in.h> 
	#include <arpa/inet.h>

	#define PORT 1234   /* Port that will be opened */ 
	#define MAXDATASIZE 100   /* Max number of bytes of data */ 

	main() 
	{ 
	int sockfd; /* socket descriptors */ 
	struct sockaddr_in server; /* server's address information */ 
	struct sockaddr_in client; /* client's address information */ 
	socklen_t sin_size; 
	int num;
	char recvmsg[MAXDATASIZE];  /* buffer for message */
	char sendmsg[MAXDATASIZE];
	char condition[] = "quit";
	/* Creating UDP socket  */
	if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)  {
	/* handle exception */
	perror("Creating socket failed.");
	exit(1);
	}

	bzero(&server,sizeof(server));
	server.sin_family=AF_INET; 
	server.sin_port=htons(PORT); 
	server.sin_addr.s_addr = htonl (INADDR_ANY); 
	if (bind(sockfd, (struct sockaddr *)&server, sizeof(struct sockaddr)) == -1) { 
	/* handle exception */
	perror("Bind error.");
	exit(1); 
	}    

	sin_size=sizeof(struct sockaddr_in); 
	while (1)   {
	num = recvfrom(sockfd,recvmsg,MAXDATASIZE,0,(struct sockaddr *)&client,&sin_size);                                    

	if (num < 0){
	perror("recvfrom error\n"); 
	exit(1); 
	} 

	recvmsg[num] = '\0';
	printf("You got a message (%s) from %s\n",recvmsg,inet_ntoa(client.sin_addr) ); /* prints client's IP */
        if(strcmp(recvmsg,condition)==0) break;
 	int i=0;
	for(i = 0 ; i < num ; i ++)
	{ 
		sendmsg[i] = recvmsg[num-1-i];
	}
	sendmsg[num]='\0';  
	sendto(sockfd,sendmsg,strlen(sendmsg),0,(struct sockaddr *)&client,sin_size); 
	
	} 

	close(sockfd);   /* close listenfd */         
	}