#include <sys/types.h>#include <sys/socket.h>#include <arpa/inet.h>#include <stdio.h>#define BUFLEN 255int main(int argc, char **argv){	struct sockaddr_in peeraddr, localaddr;	int sockfd;	char recmsg[BUFLEN+1];	int socklen, n;	if(argc!=5){		printf("%s <dest IP address> <dest port> <source IP address> <source port>\n", argv[0]);		exit(0);	}	sockfd = socket(AF_INET, SOCK_DGRAM, 0);	if(sockfd<0){		printf("socket creating err in udptalk\n");		exit(1);	}	socklen = sizeof(struct sockaddr_in);	memset(&peeraddr, 0, socklen);	peeraddr.sin_family=AF_INET;	peeraddr.sin_port=htons(atoi(argv[2]));	if(inet_pton(AF_INET, argv[1], &peeraddr.sin_addr)<=0){		printf("Wrong dest IP address!\n");		exit(0);	}	memset(&localaddr, 0, socklen);	localaddr.sin_family=AF_INET;	if(inet_pton(AF_INET, argv[3], &localaddr.sin_addr)<=0){		printf("Wrong source IP address!\n");		exit(0);	}	localaddr.sin_port=htons(atoi(argv[4]));	if(bind(sockfd, &localaddr, socklen)<0){			printf("bind local address err in udptalk!\n");		exit(2);	}	if(fgets(recmsg, BUFLEN, stdin) == NULL) exit(0);	if(sendto(sockfd, recmsg, strlen(recmsg), 0, &peeraddr, socklen)<0){		printf("sendto err in udptalk!\n");		exit(3);	}	for(;;){		/*recv&send message loop*/		n = recvfrom(sockfd, recmsg, BUFLEN, 0, &peeraddr, &socklen);		if(n<0){			printf("recvfrom err in udptalk!\n");			exit(4);		}else{			recmsg[n]=0;			printf("peer:%s", recmsg);			}		if(fgets(recmsg, BUFLEN, stdin) == NULL) exit(0);		if(sendto(sockfd, recmsg, strlen(recmsg), 0, &peeraddr, socklen)<0){			printf("sendto err in udptalk!\n");			exit(3);		}	}}