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

struct test{
        int n;
        float x;
} ;

int main()
{int shmid,i;
 void *shmptr; // usually void; cast off it...

 fprintf(stderr,"\nNow, read entire file into shmem\n");
 // Open the file
 int fd=open("abc.txt",O_RDONLY);
 // find # bytes
 int numBytes=lseek(fd,0,SEEK_END);
 // Back to beginning
 lseek(fd,0,SEEK_SET);
 // Allocate shmem needed
 shmid=shmget(getuid(),numBytes+1,IPC_CREAT|0600);
 // Attach
 shmptr=shmat(shmid,0,0);
 // Read file into shmem with 1 read
 numBytes=read(fd,shmptr,numBytes);
 // Did it work?
 fprintf(stderr,"The file: \n %s \n",shmptr);

 // OK. Put a struct into shared memory.
 // First, cast a pointer into shmem
 struct test *a=(struct test*)(shmptr+48);
 // Fill in the members
 a->n=100;
 a->x=2.345;
 // Print from shmem
 printf("Struct Contents: The int is %d and the float is %f\n",a->n,a->x);

 // Now, print entire shmem
 printf("\nShared Memory Contents...\n");
 write(1,shmptr,numBytes);

 // Detach memory
 shmdt(shmptr);
 // Remove shmem
 shmctl(shmid,IPC_RMID,0);
 fprintf(stderr,"\nShmem Removed: \n");
}