The QNX Operating System

Listing 3 (sender.c)

/*********************************************************
***
***
***    Program to illustrate message passing under QNX.
***    Written and tested under QNX version 2.15C atp
***    Compiler used: Quantum's C compiler
***
***    This program is used to send a message to the
***    holder.c program (<a href="/showArticle.jhtml?documentID=cuj9109busigin&pgno=3">listing 2</a>). It can request that
***    holder.c provide one of the following services:
***
***    1)  Store a text string that is sent to it by this
***        task.
***    2)  Reply to this task with a previously stored
***        string.
***    3)  Have holder.c commit suicide.
***
**********************************************************/

#include <stdio.h>
#include "message.h"

main(argc, argv)
int argc;
char **argv;
{
   unsigned rtid;              /* Variable to hold
                             receiving task id    */
   struct message buff;        /* Message buffers      */

/*
   If an incorrect number of arguments have been passed to
   this program print a command usage message and exit.
*/
   if (argc != 2)
   {
      printf("\nUsage: sender <arg>");
      printf("\n\nWhere: <arg> = t=\"text string\"");
      printf("\n               (stores string)");
      printf("\n       <arg> = -query");
      printf("\n               (get stored string)");
      printf("\n       <arg> = -kill");
      printf("\n               (cause holder to die)\n");
      exit(-1);
   }

/*
   Find the task id of holder.c which will receive the
   messages from this task.
*/
   if(!(rtid = name_locate(HOLDER_NAME, 0, sizeof(buff))))
   {
      printf("\nname_locate() failed\n");
      exit(-1);
   }
/*
   Build message to send to holder.
*/
   switch ( (*arg v[1] << 8) | *(argv[1] +1) )
   {
      case ('t' << 8) | '=' :
         strcpy(buff.text, (argv[1] + 2) );
         buff.mssg_type = STORE;
         break;
      case ('-' << 8) | 'q' :
         buff.mssg_type = RETRIEVE;
         break;
      case ('-' << 8) | 'k' :
         buff.mssg_type = KILL;
         break;
      default:
         printf("\nUnidentified argument used.\n");
         exit(-1);

   }

/*
   Send holder the message and print the reply if there
   there is one.
*/

   send(rtid, &buff, &buff, sizeof(buff) );

   switch (buff.mssg_type)
   {
      case STORED:
         printf("\nMessage stored\n");
         break;
      case RETRIEVED:
         printf("\nRetrieved message [%s]\n",buff.text);
         break;
      case KILL:
         printf("\nSuicide request sent to holder\n");
         break;
      default:
         printf("\nReceived unknown message [%d].\n",
                buff.mssg_type);
         break;

   }

}

/* End of File */