stack implementation - Hello World

This is not the right way to do the things..
But.. it works.. doesn't?

first a header/source file

/* 
 * file: table.h
 */
#ifndef TABLE_H
#define TABLE_H

#ifdef DATATYPE
#ifdef BTMAXSIZE

#include <stdlib.h>
#include <err.h>

struct book_strc {
  DATATYPE data;
  struct book_strc * prev;
} book_stack;


/* Book table */
static struct book_strc * book_table[BTMAXSIZE];
/* Number of stacks in table */
static unsigned int tablen = 0;


void *
xmalloc (size_t siz)
{
  register void * pool = malloc (siz);
  if (!pool)
 err (1, "xmalloc");
  return pool;
}


void
bspush (unsigned int tentry, DATATYPE val)
{
  struct book_strc * new = (struct book_strc *) xmalloc (sizeof (struct book_strc));
  new->data = val;
  new->prev = book_table[tentry];  
  tablen++;
  book_table[tentry] = new;
}

void
bspop (unsigned int tentry, DATATYPE * val)
{
  * val = book_table[tentry]->data;
  struct book_strc * tmp = book_table[tentry];
  book_table[tentry] = book_table[tentry]->prev;
  free (tmp);
  tablen--;
}

#endif
#endif
#endif

and a main program using it ..

#include <stdio.h>
#include <stdlib.h>

#define BTMAXSIZE 100
#define DATATYPE char*
#include "table.h"

int
main (void)
{
  char str1[] = "Hello";
  char str2[] = "World";
  char * str3, * str4;

  bspush (0, str1); 
  bspush (1, str2);
  bspop (1, &str4);
  bspop (0, &str3);
  printf ("%s %s\n", str3, str4);
  return 0;
}

output:
Hello World

Usage:
You declare 2 macros
BTMAXSIZE -> this is the max size of the array of stacks
DATATYPE -> this is the data type of stack objects
then you include the file table.h
this file implement a array of stacks that hold objects of same data type
The design idea is a book table where the stacks are
you can put a book at top of stack by passing the stack number and the object like
bspush (0, 100);
and then retrieve the same item by calling bspop with the number of same stack
and a address of same type object to put the result.. like:
bspop (0, &i);