IntPtr.Subtract Method (IntPtr, Int32)

.NET Framework (current version)
 
System_CAPS_noteNote

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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

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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