How to resize an array in C#

In C#, arrays cannot be resized dynamically. One approach is to use System.Collections.ArrayList instead of a native array. Another (faster) solution is to re-allocate the array with a different size and to copy the contents of the old array to the new array. The generic function resizeArray (below) can be used to do that.

// Reallocates an array with a new size, and copies the contents
// of the old array to the new array.
// Arguments:
//   oldArray  the old array, to be reallocated.
//   newSize   the new array size.
// Returns     A new array with the same contents.
public static System.Array ResizeArray (System.Array oldArray, int newSize) {
   int oldSize = oldArray.Length;
   System.Type elementType = oldArray.GetType().GetElementType();
   System.Array newArray = System.Array.CreateInstance(elementType,newSize);
   int preserveLength = System.Math.Min(oldSize,newSize);
   if (preserveLength > 0)
      System.Array.Copy (oldArray,newArray,preserveLength);
   return newArray; }

// Test routine for ResizeArray().
public static void Main () {
   int[] a = {1,2,3};
   a = (int[])ResizeArray(a,5);
   a[3] = 4;
   a[4] = 5;
   for (int i=0; i<a.Length; i++)
      System.Console.WriteLine (a[i]); }

Author: Christian d'Heureuse (,
License: Free / LGPL