Memory checking

In the previous two sections, we defined two concepts that allow us to gain confidence that:

• The pointer points to the heap.
• The pointer points to a block whose header matches that of the expected type of the pointer.

Going back to our int_stack example, we can add to our error checking as follows:

	void
	verify_int_stack(
		const char *	file,
		int		line,
		int_stack	stack
		)
	{
	  verify( file, line, is_heap_ptr(stack));
	  verify( file, line, is_heap_ptr(vals_int_stack(stack)));
	  verify( file, line, xtype_ptr(struct int_stack, stack) );
	  verify( file, line,
	  	xntype_ptr(int, max_int_stack(stack), vals_int_stack(stack)));
	  /* other verification ... */
	}

In the worst case, we can always check every access to the int stack data structure. In this case we make use of the deref_int_stack() macro.

	#define deref_int_stack(_s) \
		( assert(is_heap_ptr(_s)), \
		  assert(xtype_ptr(struct int_stack, _s)), \
		  (_s) )

Another obvious place to use these macros is just prior to freeing.

	#define xfree(_t,_p)	\
		( assert(is_heap_ptr(_p)), \
		  assert(xtype_ptr(_t, _p)), \
		  free(_p) )

	#define xnfree(_t, _n, _p)	\
		( assert(is_heap_ptr(_p)), \
		  assert(xntype_ptr(_t, _n, _p)), \
		  free(_p) )