经典vc教程的例子程序

				// Fig. 5.13: fig05_13.cpp
				// Attempting to modify a constant pointer to
				// non-constant data
				#include 
				
				int main()
				{
				   int x, y;
				
				   int * const ptr = &x; // ptr is a constant pointer to an 
				                         // integer. An integer can be modified
				                         // through ptr, but ptr always points 
				                         // to the same memory location.
				   *ptr = 7;
				   ptr = &y;
				
				   return 0;
				}