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String.TrimStart Method (Char())

 

Removes all leading occurrences of a set of characters specified in an array from the current String object.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

Public Function TrimStart (
	ParamArray trimChars As Char()
) As String

Parameters

trimChars
Type: System.Char()

An array of Unicode characters to remove, or null.

Return Value

Type: System.String

The string that remains after all occurrences of characters in the trimChars parameter are removed from the start of the current string. If trimChars is null or an empty array, white-space characters are removed instead.

The TrimStart method removes from the current string all leading characters that are in the trimChars parameter. The trim operation stops when a character that is not in trimChars is encountered. For example, if the current string is "123abc456xyz789" and trimChars contains the digits from "1" through "9", the TrimStart method returns "abc456xyz789".

System_CAPS_noteNote

If the TrimStart method removes any characters from the current instance, this method does not modify the value of the current instance. Instead, it returns a new string in which all leading white space characters found in the current instance are removed.

Notes to Callers:

The .NET Framework 3.5 SP1 and earlier versions maintains an internal list of white-space characters that this method trims if trimChars is null or an empty array. Starting with the .NET Framework 4, if trimChars is null or an empty array, the method trims all Unicode white-space characters (that is, characters that produce a true return value when they are passed to the Char.IsWhiteSpace method). Because of this change, the Trim() method in the .NET Framework 3.5 SP1 and earlier versions removes two characters, ZERO WIDTH SPACE (U+200B) and ZERO WIDTH NO-BREAK SPACE (U+FEFF), that the Trim() method in the .NET Framework 4 and later versions does not remove. In addition, the Trim() method in the .NET Framework 3.5 SP1 and earlier versions does not trim three Unicode white-space characters: MONGOLIAN VOWEL SEPARATOR (U+180E), NARROW NO-BREAK SPACE (U+202F), and MEDIUM MATHEMATICAL SPACE (U+205F).

The following example uses the TrimStart method to trim white space and comment characters from lines of source code. The StripComments method wraps a call to TrimStart and passes it a character array that contains a space and the comment character, which is an apostrophe ( ' ) in Visual Basic and a slash ( / ) in C#. The TrimStart method is also called to remove leading white space when evaluating whether a string is a comment.

Public Shared Function StripComments(lines() As String) As String()
   Dim lineList As New List(Of String)
   For Each line As String In lines
      If line.TrimStart(" "c).StartsWith("'") Then
         linelist.Add(line.TrimStart("'"c, " "c))
      End If
   Next
   Return lineList.ToArray()
End Function   

The following example then illustrates a call to the StripComments method.

Public Shared Sub Main()
   Dim lines() As String = {"Public Module HelloWorld", _
                            "   Public Sub Main()", _
                            "      ' This code displays a simple greeting", _
                            "      ' to the console.", _
                            "      Console.WriteLine(""Hello, World."")", _
                            "   End Sub", _
                            " End Module"}
   Console.WriteLine("Code before call to StripComments:")
   For Each line As String In lines
      Console.WriteLine("   {0}", line)                         
   Next                            

   Dim strippedLines() As String = StripComments(lines) 
   Console.WriteLine("Code after call to StripComments:")
   For Each line As String In strippedLines
      Console.WriteLine("   {0}", line)                         
   Next                            
End Sub
' This code produces the following output to the console:
'    Code before call to StripComments:
'       Public Module HelloWorld
'          Public Sub Main()
'             ' This code displays a simple greeting
'             ' to the console.
'             Console.WriteLine("Hello, World.")
'          End Sub
'       End Module
'    Code after call to StripComments:
'       This code displays a simple greeting
'       to the console.   

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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