Redim Preserve in C#?

I was shocked to find out today that C# does not support dynamic sized arrays. How then does a VB.NET developer used to using ReDim Preserve deal with this in C#?

At the beginning of the function I am not sure of the upper bound of the array. This depends on the rows returned from the database.


Use ArrayLists or Generics instead

VB.NET doesn't have the idea of dynamically sized arrays, either - the CLR doesn't support it.

The equivalent of "Redim Preserve" is Array.Resize<T> - but you must be aware that if there are other references to the original array, they won't be changed at all. For example:

using System;

class Foo
    static void Main()
        string[] x = new string[10];
        string[] y = x;

        Array.Resize(ref x, 20);
        Console.WriteLine(x.Length); // Prints out 20
        Console.WriteLine(y.Length); // Still prints out 10

Proof that this is the equivalent of Redim Preserve:

Imports System

Class Foo
    Shared Sub Main()
        Dim x(9) as String
        Dim y as String() = x

        Redim Preserve x(19)
    End Sub
End Class

The two programs are equivalent.

If you truly want a dynamically sized collection, you should use List<T> (or something similar). There are various issues with using arrays directly - see Eric Lippert's blog post for details. That's not to say you should always avoid them, by any means - but you need to know what you're dealing with.

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