IntPtr.Subtract(IntPtr, Int32) IntPtr.Subtract(IntPtr, Int32) IntPtr.Subtract(IntPtr, Int32) IntPtr.Subtract(IntPtr, Int32) Method

Definition

Subtracts an offset from the value of a pointer.

public:
 static IntPtr Subtract(IntPtr pointer, int offset);
public static IntPtr Subtract (IntPtr pointer, int offset);
static member Subtract : nativeint * int -> nativeint
Public Shared Function Subtract (pointer As IntPtr, offset As Integer) As IntPtr

Parameters

pointer
IntPtr IntPtr IntPtr IntPtr

The pointer to subtract the offset from.

offset
Int32 Int32 Int32 Int32

The offset to subtract.

Returns

A new pointer that reflects the subtraction of offset from pointer.

Examples

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
Imports System.Runtime.InteropServices

Module Example
   Public Sub Main()
      Dim arr() As Integer = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20}
      Dim ptr As IntPtr = Marshal.UnsafeAddrOfPinnedArrayElement(arr, arr.Length - 1)
      Dim size As Integer = Len(arr(0))

      For ctr As Integer = 0 To arr.Length - 1
         Dim newPtr As IntPtr = IntPtr.Subtract(ptr, ctr * size)
         Console.Write("{0}   ", Marshal.ReadInt32(newPtr))
      Next
   End Sub
End Module
' The example displays the following output:
'       20   18   16   14   12   10   8   6   4   2

Remarks

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.

Applies to

See also