1 /* timeclnt.c - a client for timeserv.c 2  *              usage: timeclnt hostname portnumber 3  */ 4 #include <stdio.h> 5 #include <sys/types.h> 6 #include <sys/socket.h> 7 #include <netinet/in.h> 8 #include <netdb.h> 9 10 #define oops(msg) {perror(msg); exit(1); }11 #define oopsn(msg, x) {perror(msg); exit(x);};12 int main(int argc, char* argv[]) {13   struct sockaddr_in servadd; 14   struct hostent *hp;15   int sock_id, sock_fd;16   char message[BUFSIZ];17   int messlen;18   int connect_num;19   /*** Step 1: Get a socket ***/20   sock_id=socket(PF_INET, SOCK_STREAM, 0);21   if(sock_id==-1)22     oops("socket");23   /*** Step 2: connect to server need to build address (host, port)of server first ***/24   bzero((void*)&servadd, sizeof(servadd));25   hp=gethostbyname(argv[1]);26   if(hp==NULL)27     oops(argv[1]);28 29   bcopy(hp->h_addr, (struct sockaddr*)&servadd.sin_addr, hp->h_length);30   servadd.sin_port=htons(atoi(argv[2]));/**这里记住一定要atoi转换，不然connect不起**/31   servadd.sin_family=AF_INET;32 33   if((connect_num=connect(sock_id, (struct sockaddr*)&servadd, sizeof(servadd)))!=0)34     {  35       printf("connect fail is %d.",connect_num);36       oopsn("connnnnect!!!!!", connect_num);37     }38   39   /*** Step 3: transfer data from server , then hangup ***/40   messlen=read(sock_id, message, BUFSIZ);41   if(messlen == 1)42     oops("read");43   if(write(1, message, messlen)!= messlen)44     oops("write");45   close(sock_id);46   return 0;47 }