#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/msg.h>#include <signal.h>#include <time.h>#define KEYPATH "/root/chat"#define NAMESIZE 16#define MSGSIZE 128#define LEN sizeof(int)+sizeof(int)+NAMESIZE+MSGSIZE#define SERTYPE 1// subtype#define NORMAL 0#define REGISTER 1#define UNREGISTER -1struct msgbuf{    long mtype;    int subtype;    int id;    char nickname[NAMESIZE];    char mtext[MSGSIZE];}buf_in, buf_out;int main(int argc, char **argv){   int msgid,pid;   key_t key;   if ( argc != 2 )   {      fprintf(stdout, "Usage: %s <name> \n", argv[0]);      exit(1);   }   if ( (key=ftok(KEYPATH, 'c')) == -1 )   {      printf("faile to locate %s\n", KEYPATH);      exit(-1);   }   msgid = msgget(key, 0666);   if ( msgid == -1 )   {      printf("Be sure server is on...\n");      exit(-1);   }// register to the server   buf_out.mtype = SERTYPE;   buf_out.subtype = REGISTER;   buf_out.id = getpid();   strcpy(buf_out.nickname, argv[1]);   memset(buf_out.mtext, 0, MSGSIZE);   if ( msgsnd(msgid, &buf_out, LEN, 0) == -1 )   {       perror("Failed to register");      exit(-1);   }   if ( (pid = fork()) == -1 )   {      perror("fork:");      exit(-1);   }   if ( pid > 0 )   // parent process   {      while(1)      {         printf("\nPlease input message:");          fgets(buf_out.mtext, MSGSIZE, stdin);         if ( strncmp(buf_out.mtext,"quit",4) == 0 )         {            kill(pid, SIGQUIT);            buf_out.subtype = UNREGISTER;            if ( msgsnd(msgid, &buf_out, LEN, 0) == -1 )            {                  perror("can't send message...");            }              exit(0);         }         buf_out.subtype = NORMAL;         if ( msgsnd(msgid, &buf_out, LEN, 0) == -1 )         {            perror("can't send message...");          }       }   }   else                  // child process   {      while ( 1 )      {         if ( msgrcv(msgid, &buf_in, LEN, getppid(), 0) == -1 )         {            printf("\ncan't receive message, maybe server is down. exit...\n");            kill(getppid(), SIGINT);            sleep(1);            exit(-1);         }          if ( buf_in.subtype == NORMAL )         {              printf("\n[%s] %s\n", buf_in.nickname, buf_in.mtext);         }         else         {             printf("\n[%s %s]\n", buf_in.nickname, buf_in.mtext);          }            }   }}