服務器端代碼：#include <stdio.h>#include <strings.h>#include <unistd.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#define PORT 1234#define BACKLOG 1int main(){? ? int listenfd,connectfd;? ? struct sockaddr_in server;? ? struct sockaddr_in client;? ? socklen_t addrlen;? ??? ? if((listenfd=socket(AF_INET,SOCK_STREAM,0))==-1)? ? {? ? ? ? perror("socket() error.");? ? ? ? exit(1);? ? }? ? 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)? ? {? ? ? ? perror("Bind() error");? ? ? ? exit(1);? ? }? ? if(listen(listenfd,BACKLOG)==-1)? ? {? ? ? ? perror("listen() error.\n");? ? ? ? exit(1);? ? }? ? int len=sizeof(client);? ? if((connectfd==accept(listenfd,(struct sockaddr *)&client,&addrlen))==-1)? ? {? ? ? ? perror("accept() error\n");? ? ? ? exit(1);? ? }? ? printf("You got a connection from client's ip is %s, port is %d\n",inet_ntoa(client.sin_addr),ntohs(client.sin_port));? ? send(connectfd,"Welcome\n",8,0);? ? close(connectfd);? ? close(listenfd);}客戶端代碼：#include <stdio.h>#include <unistd.h>#include <strings.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <netdb.h>#define PORT 1234#define MAXDATASIZE 100int main(int argc,char *argv[]){? ? int sockfd,num;? ? char buf[MAXDATASIZE];? ? struct hostent *he;? ? 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);? ? }? ? 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);}為什么我客戶端用127.0.0.1測試的時候，客戶端不輸出服務器發給客戶端的Welcone