TITLE: cheating on array bounds


[ This article adapted from "Cheating on Array Bounds", Andrew Koenig,
  C++ Report, V7 N4, p. 12 ]


Here is a common C trick:

	struct string
	{
		int  length;
		char data [1];
	};


	string* p2 = ...
	...
	struct string s = malloc (sizeof (struct string) + p2->length - 1);
	s->length = p2->length;
	strncpy (s->data, p2->data, p2->length);
	...
	free (s);
	...

This is a really bad idea in C++. Suppose we had a C++ version of 
this as

	struct string
	{
		virtual void foo ();

		int length;
		char data [1];
	};

It is a common implementation technique to implement this struct
as if it were declared as

	struct string
	{
		int length;
		char data [1];
		virtual_table *vptr;
	};

The virtual table pointer would be wiped out by using the above
technique. In short, respect array bounds if you code in C++.