#include <stdio.h>
#include <stdlib.h>
#include <sys/shm.h>

#define SHMKEY           1000

typedef struct _DATA  {
    int  value;
    char sText[ 50 ];
} DATA, *PDATA;

int g_shmid;

int main( void )
{
    int   i;
    PDATA pdata;

    /* create the shared memory segment and get its id */
    g_shmid = shmget( SHMKEY, sizeof( DATA ), 0644 | IPC_CREAT );

    /* bail out if it failed */
    if ( -1 == g_shmid )  {
        perror( "shared memory create" );
        exit( EXIT_FAILURE );
    }

    /* get a pointer to the shared memory */
    pdata = (PDATA) shmat( g_shmid, 0, 0 );

    /* create a child process */
    if ( 0 == fork() )  {
        if ( -1 == (int) pdata )
            perror( "child memory attach" );
        else  {
            /* put some data in the structure */
            srand( time( NULL ) );
            pdata->value = rand();
            strcpy( pdata->sText, "Hi, dad!" );
            printf( "Child:  value=%d  text='Hi, dad!'\n", pdata->value );

            /* detach the memory from this process */
            shmdt( (char*) pdata );
        }
    }
    else  {
        /* let child go first */
        wait( 0 );

        if ( -1 == (int) pdata )
            perror( "parent memory attach" );
        else  {
            /* print out whatever is in the structure */
            printf( "Parent: value=%d  text='%s'\n", pdata->value, 
                    pdata->sText );

            /* detach the memory from this process */
            shmdt( (char*) pdata );

            /* destroy the segment--note that this is only
             * done in the parent and after the child has finished 
             */
            if ( -1 == shmctl( g_shmid, IPC_RMID, NULL ) )
                perror( "shared memory delete" );
        }
    }
}