Статья
11/17/2011

String.TrimStart Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

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

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

Syntax

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

public string TrimStart(
    params char[] trimChars
)

Parameters

trimChars
Type: array<System.Char[]
An array of Unicode characters to remove or nulla null reference (Nothing in Visual Basic).

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 nulla null reference (Nothing in Visual Basic) or an empty array, white-space characters are removed instead.

Remarks

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".

Note:
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.

For more information about which Unicode characters are categorized as white-space characters, see the Remarks section of the String.Trim() method overload.

Examples

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 (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(ByVal 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

public static string[] StripComments(string[] lines)
{
   List<string> lineList = new List<string>();
   foreach (string line in lines)
   {
      if (line.TrimStart(' ').StartsWith("//"))
         lineList.Add(line.TrimStart(' ', '/'));
   }
   return lineList.ToArray();
}

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

Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
   Dim lines() As String = {"Public Module HelloWorld", _
                            "   Public Sub Main()", _
                            "      ' This code displays a simple greeting", _
                            "      '.", _
                            "      outputBlock.Text += String.Format(""Hello, World."") & vbCrLf", _
                            "   End Sub", _
                            " End Module"}
   outputBlock.Text &= "Code before call to StripComments:" & vbCrLf
   For Each line As String In lines
      outputBlock.Text += String.Format("   {0}", line) & vbCrLf
   Next

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

public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
   string[] lines = {"using System;",
                    "", 
                    "public class HelloWorld",
                    "{", 
                    "   public static void Main()",
                    "   {", 
                    "      // This code displays a simple greeting", 
                    "      //.", 
                    "      outputBlock.Text += String.Format(\"Hello, World.\")", 
                    "   }", 
                    "}"};
   outputBlock.Text += "Before call to StripComments:" + "\n";
   foreach (string line in lines)
      outputBlock.Text += String.Format("   {0}", line) + "\n";

   string[] strippedLines = StripComments(lines);
   outputBlock.Text += "After call to StripComments:" + "\n";
   foreach (string line in strippedLines)
      outputBlock.Text += String.Format("   {0}", line) + "\n";
}
// This code produces the following output:
//    Before call to StripComments:
//       using System;
//   
//       public class HelloWorld
//       {
//           public static void Main()
//           {
//               // This code displays a simple greeting
//               //.
//               Console.WriteLine("Hello, World.");
//           }
//       }  
//    After call to StripComments:
//       This code displays a simple greeting
//      .

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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