VB.NET - String.Copy and CopyTo

Array Char Array For Shared

String.Copy, CopyTo. Usually a string does not need copying. We can use literals, or the strings returned by methods like Replace or ToString.

With Copy, we copy an existing string and get a new string. With CopyTo we copy the characters of a string into a Char array. We specify an index and length.

Copy example. The String.Copy method receives a string and returns a copy of that string. This is a shared method—we do not call it on a string instance.

Here We use ReferenceEquals to see if two variables point to the same reference. String.Copy returns a separate, new string.

Module Module1

    Sub Main()
        Dim value As String = "cat"

        ' Use String.Copy to copy a string.
        Dim valueCopied As String = String.Copy(value)

        ' The copy has a different reference.
        If Not ReferenceEquals(value, valueCopied) Then
            Console.WriteLine("Not same reference")
        End If
    End Sub

End Module
Not same reference

CopyTo. This method has nothing in common with String.Copy. CopyTo is an instance method and it copies the string's characters to a char array.

Here We copy the first 3 characters in a string to a 3-element char array. We then use For-Each to display the array's contents.

Tip In VB.NET we use the last array index to indicate its length. So a 2 means a 3-element array.

Module Module1

    Sub Main()
        Dim value As String = "dog"

        ' A 3-element char array.
        Dim destination(2) As Char

        ' Copy string to the destination array.
        value.CopyTo(0, destination, 0, 3)

        ' Loop over the resulting char array.
        For Each letter As Char In destination
            Console.WriteLine(letter)
        Next
    End Sub

End Moduled
o
g

A summary. The String.Copy and CopyTo methods provide ways to get the contents of strings and put them in new objects. CopyTo is more useful—it helps use char arrays.

As developers we rarely need to use String.Copy. But it is helpful to know it exists. To reduce memory usage, it is best to reuse existing strings.

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This page was last updated on Nov 7, 2023 (edit).

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