Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
Subtract Method

IntPtr.Subtract Method

.NET Framework 4.6 and 4.5

Subtracts an offset from the value of a pointer.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static IntPtr Subtract(
	IntPtr pointer,
	int offset
)

Parameters

pointer
Type: System.IntPtr

The pointer to subtract the offset from.

offset
Type: System.Int32

The offset to subtract.

Return Value

Type: System.IntPtr
A new pointer that reflects the subtraction of offset from pointer.

The Subtract method does not throw an exception if the result is too small to represent as a pointer on the specified platform. Instead, the subtraction operation is performed in an unchecked context.

Languages that do not support operator overloading or custom operators can use this method to subtract an offset from the value of a pointer.

The following example instantiates an IntPtr object that points to the end of a ten-element array, and then calls the Subtract method to iterate the elements in the array in reverse order.

using System;
using System.Runtime.InteropServices;

public class Example
{
   public static void Main()
   {
      int[] arr = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20};
      // Get the size of a single array element. 
      int size = sizeof(int);
      unsafe {
         fixed(int* pend = &arr[arr.GetUpperBound(0)]) {
            IntPtr ptr = new IntPtr(pend);
            for (int ctr = 0; ctr < arr.Length; ctr++)
            {
               IntPtr newPtr = IntPtr.Subtract(ptr, ctr * size);
               Console.Write("{0}   ", Marshal.ReadInt32(newPtr));
            }
         }
      }
   }
}
// The example displays the following output: 
//       20   18   16   14   12   10   8   6   4   2

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
Show:
© 2015 Microsoft