/*
 * shmread.c
 * Reads a message from a shared memory segment.
 */

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

#define MAX_SIZE 512

int main(int argc, char **argv)
{
	key_t key;
	int shm;
	void *ptr;
	char buffer[512];

	if((key=ftok("sharedmem",'a'))==-1)
	{
		fprintf(stdout,"failed to get key for shared memory segment %d, %s\n",errno,strerror(errno));
		fflush(stdout);
		return -1;
	}

	if((shm=shmget(key,MAX_SIZE, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP))==-1)
	{
		fprintf(stdout,"failed to allocate shared memory segment %d, %s\n",errno,strerror(errno));
		fflush(stdout);
		return -1;
	}

	fprintf(stdout,"shared memory segment %x allocated\n",key);
	fflush(stdout);

	if(((int)(ptr=shmat(shm,NULL,0)))==-1)
	{
		fprintf(stdout,"failed to attach shared memory segment to pointer %d, %s\n",errno,strerror(errno));
		fflush(stdout);
		return -1;
	}

	strcpy(buffer,ptr);

	fprintf(stdout,"memory contents: %s\n",buffer);

	if(shmdt(ptr)==-1)
	{
		fprintf(stdout,"failed to dettached pointer from shared memory segment %d, %s\n",errno,strerror(errno));
		fflush(stdout);
		return -1;
	}

	return 0;
}