ssize_t recvfrom(int s, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen);ssize_t sendto(int s, const void *buf, size_t len, int flags, struct sockaddr *to, socklen_t tolen);

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <arpa/inet.h>
#define MAX_MSG_SIZE 1024int main(int argc,char** argv){int skfd,addrlen,ret;struct sockaddr_in addr,cltaddr;char buf[MAX_MSG_SIZE]={0};char sndbuf[MAX_MSG_SIZE]={0};//创建数据报式套接字skfdif(0>(skfd=socket(AF_INET,SOCK_DGRAM,0))){perror("Create Error");exit(1);}bzero(&addr,sizeof(struct sockaddr_in));addr.sin_family = AF_INET;addr.sin_addr.s_addr=htonl(INADDR_ANY);addr.sin_port=htons(atoi(argv[1]));//将socket文件描述符skfd和本地端口和地址绑定起来if(0>(bind(skfd,(struct sockaddr*)&addr,sizeof(struct sockaddr_in)))){perror("Bind Error");exit(1);}//开始收发数据while(1){ret=recvfrom(skfd,buf,MAX_MSG_SIZE,0,(struct sockaddr*)&cltaddr,&addrlen);if(ret < 0){printf("recv data from %s:%d error!",inet_ntoa(cltaddr.sin_addr),ntohs(cltaddr.sin_port));}else if(ret == 0){perror("client has been closing socket!");}else{printf("From %s:%d,%s",inet_ntoa(cltaddr.sin_addr),ntohs(cltaddr.sin_port),buf);memset(sndbuf,0,MAX_MSG_SIZE);switch(buf[0]){case 'a':strcpy(sndbuf,"After u ,lady...");break;case 'b':strcpy(sndbuf,"Before u ,sir...");break;case 'c':strcpy(sndbuf,"Can u?");break;default:strcpy(sndbuf,"I dont't know what u want!");}sendto(skfd,sndbuf,strlen(sndbuf),0,(struct sockaddr*)&cltaddr,addrlen);}memset(buf,0,MAX_MSG_SIZE);}return 0;
}

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <arpa/inet.h>
#define MAX_MSG_SIZE 1024int main(int argc,char** argv){int skfd,ret,len;struct sockaddr_in srvaddr;char buf[MAX_MSG_SIZE]={0};char sndbuf[MAX_MSG_SIZE]={0};struct in_addr addr;//创建数据报式套接字skfdif(0>(skfd=socket(AF_INET,SOCK_DGRAM,0))){perror("Create Error");exit(1);}if(0 == inet_aton(argv[1],&addr)){perror("server addr invalid!");exit(1);}bzero(&srvaddr,sizeof(struct sockaddr_in));srvaddr.sin_family = AF_INET;srvaddr.sin_addr=addr;srvaddr.sin_port=htons(atoi(argv[2]));//我们的客户端只接收从服务器地址是srvaddr的主机发来的数据if(0>(connect(skfd,(struct sockaddr*)&srvaddr,sizeof(struct sockaddr_in)))){perror("Connect Error");exit(1);}//开始收发数据while(1){memset(sndbuf,0,MAX_MSG_SIZE);len=read(0,sndbuf,MAX_MSG_SIZE);ret=sendto(skfd,sndbuf,strlen(sndbuf),0,(struct sockaddr*)&srvaddr,sizeof(struct sockaddr));if(ret == len){memset(buf,0,MAX_MSG_SIZE);//我们已经知道服务器地址信息了，所以最后两个参数为NULLret=recvfrom(skfd,buf,MAX_MSG_SIZE,0,NULL,NULL);if(ret < 0){perror("read error from server!");}else if(ret == 0){perror("server has been closing socket!");}else{buf[ret]='\0';printf("From Server:%s\n",buf);}}}return 0;
}