Concatenating Strings Efficiently

StringBuilders should be reserved when the number of concatenations is unknown or large. 
Strings are immutable (not allowed to be changed). 

Dim sampleString As String = "I think the vegetables are : " _

sampleString &= "Tasty"

In the above example, the compiler will create a new string, allocate memory, copy the data from the original string and then copying the new data at the end of the existing string.

For a large number of concatenations, this operation is inefficient.


The performance of a concatenation operation for a String or StringBuilder object depends on how often a memory allocation occurs. A string concatenation operation always allocates memory, whereas a StringBuilder concatenation operation only allocates memory if the StringBuilder object buffer is too small to accommodate the new data.

Dim sampleString As String = "I think the vegetables are : " _

& "Tasty"

The string class is preferable if a fixed number of string objects are concatenated. Individual concatenation operations might be optmized by the compiler into a single operation.

 

Public Function Reproduce(

ByVal source As String,

ByVal iterations As Integer) As String

      Dim sampleStringBuilder As New System.Text.StringBuilder()

        For index As Integer = 0 To iterations

            sampleStringBuilder.Append(source)

        Next

      Return sampleStringBuilder.ToString()

End Function

A StringBuilder implementation is preferred when a large or unknown number of strings needs to be concatenated.


Resources:

http://www.yoda.arachsys.com/csharp/stringbuilder.html

http://msdn.microsoft.com/en-us/library/system.text.stringbuilder.aspx