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String.IndexOf Method (String, Int32, Int32)

Reports the zero-based index of the first occurrence of the specified string in this instance. The search starts at a specified character position and examines a specified number of character positions.

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

'Declaration
Public Function IndexOf ( _
	value As String, _
	startIndex As Integer, _
	count As Integer _
) As Integer

Parameters

value
Type: System.String

The string to seek.

startIndex
Type: System.Int32

The search starting position.

count
Type: System.Int32

The number of character positions to examine.

Return Value

Type: System.Int32
The zero-based index position of value if that string is found, or -1 if it is not. If value is String.Empty, the return value is startIndex.

ExceptionCondition
ArgumentNullException

value is Nothing.

ArgumentOutOfRangeException

count or startIndex is negative.

-or-

startIndex is greater than the length of this string.

-or-

count is greater than the length of this string minus startIndex.

Index numbering starts from 0 (zero). The startIndex parameter can range from 0 to the length of the string instance.

This method performs a word (case-sensitive and culture-sensitive) search using the current culture. The search begins at startIndex and continues to startIndex + count -1. The character at startIndex + count is not included in the search.

Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed. If value consists only of one or more ignorable characters, the IndexOf(String, Int32, Int32) method always returns startIndex, which is the character position at which the search begins. In the following example, the IndexOf(String, Int32, Int32) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting in the third through sixth character positions in two strings. Only one of the strings contains the required substring. If the example is run on the .NET Framework 4 or later, in both cases, because the soft hyphen is an ignorable character, the method returns the index of "m" in the string when it performs a culture-sensitive comparison. Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m".

Module Example
   Public Sub Main()
      Dim searchString As String = Chrw(&h00AD) + "m" 
      Dim s1 As String = "ani" + ChrW(&h00AD) + "mal" 
      Dim s2 As String = "animal"

      Console.WriteLine(s1.IndexOf(searchString, 2, 4))
      Console.WriteLine(s2.IndexOf(searchString, 2, 4))
   End Sub 
End Module 
' The example displays the following output: 
'       4 
'       3

Notes to Callers

As explained in Best Practices for Using Strings in the .NET Framework, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. To use the comparison rules of the current culture to perform this operation, call the IndexOf(String, Int32, Int32, StringComparison) method overload with a value of StringComparison.CurrentCulture for its comparisonType parameter.

The following example finds the index of all occurrences of the string "he" within a substring of another string. Note that the number of characters to be searched must be recalculated for each search iteration.

' Sample for String.IndexOf(String, Int32, Int32) 
Imports System

Class Sample

   Public Shared Sub Main()

      Dim br1 As String = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-" 
      Dim br2 As String = "0123456789012345678901234567890123456789012345678901234567890123456" 
      Dim str As String = "Now is the time for all good men to come to the aid of their party." 
      Dim start As Integer 
      Dim at As Integer 
      Dim [end] As Integer 
      Dim count As Integer

      [end] = str.Length
      start = [end] / 2
      Console.WriteLine()
      Console.WriteLine("All occurrences of 'he' from position {0} to {1}.", start, [end] - 1)
      Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str)
      Console.Write("The string 'he' occurs at position(s): ")

      count = 0
      at = 0
      While start <= [end] AndAlso at > - 1
         ' start+count must be a position within -str-.
         count = [end] - start
         at = str.IndexOf("he", start, count)
         If at = - 1 Then 
            Exit While 
         End If
         Console.Write("{0} ", at)
         start = at + 1
      End While
      Console.WriteLine()
   End Sub 'Main
End Class 'Sample

'This example produces the following results: 

'All occurrences of 'he' from position 33 to 66. 
'0----+----1----+----2----+----3----+----4----+----5----+----6----+- 
'0123456789012345678901234567890123456789012345678901234567890123456 
'Now is the time for all good men to come to the aid of their party. 

'The string 'he' occurs at position(s): 45 56 

'

.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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