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/* CopyRight GPL 2004 mmc Mike Chirico mchirico@users.sourceforge.net
   
   Demonstrates usage of SystemV Message Queues on Linux 2.4

Compile:
   g++ msg_Q_write.cc -o qwrite
   g++ msg_Q_read.cc -o qread

Reference:
http://cvs.sourceforge.net/viewcvs.py/cpearls/cpearls/src/posted_on_sf/msg_Q

Download:
http://ftp1.sourceforge.net/cpearls/msg_Q.tar.gz

*/
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>
#include <errno.h>


using namespace std;

const char SEED = 'M';
const long int SERVER=1L;
typedef struct {
  long int msg_to;
  long int msg_fm;               // Complete size of the message is 8192 = buffer + 2* long int 
  char buffer[BUFSIZ - 2*sizeof(long int) ]; //BUFSIZ is usually 8192.  $/sbin/sysctl -A
} MESSAGE;             // But note...default max size of queue (bytes) = 16384
                       // You'll only get 2 messages of this size in the queue!
                       // So don't send messages size BUFSIZ if they are only
                       // padded with zeros.




extern int errno;
int Mkdir(string s)
{
  if ( mkdir(s.c_str(), 0660) == -1) 
    {
      if (errno != EEXIST)
	{
	  perror("Can't create and doesn't exist: ");
	  exit(-1);
	}
    }
  return 1;
}

key_t Ftok(string s,char c)
{
  key_t key;
  if (( key = ftok(s.c_str(),c)) == -1) {
    perror("key generation");
    exit(-2);
  }
  return key;
}
int main(void)
{
  string s;
  pid_t client_pid;
  int   mid, n;
  MESSAGE msg;
  key_t key;


  s="/tmp/message_queues";
  Mkdir(s);
  key=Ftok(s,'a');
  cout << "key= " << key << endl;

  if (( mid=msgget(key,IPC_CREAT|0660)) == -1 )
    {
      if(errno != EEXIST)
	{
	  perror("Message queue problems");
	  exit(-1);
	}
    }
  // Here it already exists
  client_pid= getpid();
  msg.msg_to = 5;
  msg.msg_fm = client_pid;
  while(1)
    {
      memset(msg.buffer, 0x0, BUFSIZ- 2*sizeof(long int));
      if ( ( n=read(fileno(stdin), msg.buffer, BUFSIZ- 2*sizeof(long int))) <= 0)
	break;
      else
	msg.buffer[n-1]='\0';
      fprintf(stderr,"Read in %d strlen=%d  ->%s<-\n",n,strlen(msg.buffer),msg.buffer);
      if ( msgsnd(mid, &msg, BUFSIZ, 0) == -1)
	{
	  perror("msgsend error:");
	}
    }

      

  
 
}





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Chirico img Mike Chirico, a father of triplets (all girls) lives outside of Philadelphia, PA, USA. He has worked with Linux since 1996, has a Masters in Computer Science and Mathematics from Villanova University, and has worked in computer-related jobs from Wall Street to the University of Pennsylvania. His hero is Paul Erdos, a brilliant number theorist who was known for his open collaboration with others.


Mike's notes page is souptonuts. For open source consulting needs, please send an email to mchirico@gmail.com. All consulting work must include a donation to SourceForge.net.

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