#include	<sys/types.h>
#include	<sys/ipc.h>
#include	<sys/shm.h>
#include	<errno.h>
#include	<stdio.h>

int
get_shmid( key_t shmkey, int size, int * just_created )
{
	int		f1 = 0666 | IPC_CREAT | IPC_EXCL;
	int		f2 = 0666;
	int		shmid;

	if ( (shmid = shmget( shmkey, size, f1 )) != -1 )
	{
		*just_created = 1;
		return shmid;
	}
	else if ( (shmid = shmget( shmkey, size, f2 )) != -1 )
	{
		*just_created = 0;
		return shmid;
	}
	else
	{
		return -1;
	}
}

#define ID 1112232448

void *
get_shmem( int size, int * just_created, int * shmid )
{
	key_t		shmkey;
	char *		p;

	errno = 0;
	if ( (shmkey = ftok( "/tmp", ID )) == -1 )
	{
		printf( "ftok failed\n" );
		return 0;
	}
	else if ( (*shmid = get_shmid( shmkey, 200, just_created )) == -1 )
	{
		printf( "get_shmid failed\n" );
		return 0;
	}
	else if ( (p = shmat( *shmid, NULL, 0 )) == (void *)-1 )
	{
		printf( "shmat failed\n" );
		return 0;
	}
	else
	{
		return p;
	}
}

int
main()
{
	char *			p;
	int			just_created;
	int			shmid;
	char			message[] = "I'm Gumby, dammit...";

	if ( (p = (char *)get_shmem( 200, &just_created, &shmid )) == 0 )
	{
		printf( "get_shmem() failed.\n" );
		return 0;
	}
	else if ( just_created )
	{
		memcpy( p, message, sizeof(message) );
		printf( "Putting message into shared memory.\n" );
		return 0;
	}
	else
	{
		printf( "Getting message from shared memory:  %s\n", p );
		shmdt( p );
		shmctl( shmid, IPC_RMID, NULL );
		return 0;
	}
}