C# Cookbook

16.2. Comparing Pointers

Problem

You need to know whether two pointers point to the same memory location. If they don’t, you need to know which of the two pointers points to a higher or lower element in the same block of memory.

Solution

Using the == and != operators, we can determine if two pointers point to the same memory location. For example, the code:

unsafe 
{
    int[] arr = new int[5] {1,2,3,4,5};
    fixed(int* ptrArr = &arr[0])
    {
        int* p1 = (ptrArr + 1);
        int* p2 = (ptrArr + 3);

        Console.WriteLine("p2 > p1");
        Console.WriteLine("(p2 == p1) = " + (p2 == p1));
        Console.WriteLine("(p2 != p1) = " + (p2 != p1));

        p2 = p1;
        Console.WriteLine("p2 == p1");
        Console.WriteLine("(p2 == p1) = " + (p2 == p1));
        Console.WriteLine("(p2 != p1) = " + (p2 != p1));
    }
}

displays the following:

p2 > p1
(p2 == p1) = False
(p2 != p1) = True

p2 == p1
(p2 == p1) = True
(p2 != p1) = False

Using the >, <, >=, or <= comparison operators, we can determine whether two pointers are pointing to a higher, lower, or the same element in an array. For example, the code:

unsafe { int[] arr = new int[5] {1,2,3,4,5}; fixed(int* ptrArr = &arr[0]) { int* p1 = (ptrArr + 1); int* p2 = (ptrArr + 3); Console.WriteLine("p2 > p1"); Console.WriteLine("(p2 > p1) = " + (p2 > p1)); Console.WriteLine("(p2 < p1) = " + (p2 < p1)); Console.WriteLine("(p2 >= p1) = " + (p2 >= p1)); Console.WriteLine("(p2 <= p1) = " + (p2 <= p1)); p2 = p1; Console.WriteLine("p2 == p1"); Console.WriteLine("(p2 > p1) = " + (p2 > p1)); Console.WriteLine("(p2 ...