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String.TrimStart Method

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)

'Declaration
Public Function TrimStart ( _
	ParamArray trimChars As Char() _
) As String

Parameters

trimChars
Type: System.Char()

An array of Unicode characters to remove, or Nothing.

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 Nothing 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".

NoteNote

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 Nothing or an empty array. Starting with the .NET Framework 4, if trimChars is Nothing 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.   

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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