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String.IndexOf Method (Char, Int32, Int32)

Reports the zero-based index of the first occurrence of the specified character 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)

Public Function IndexOf ( _
	value As Char, _
	startIndex As Integer, _
	count As Integer _
) As Integer


Type: System.Char

A Unicode character to seek.

Type: System.Int32

The search starting position.

Type: System.Int32

The number of character positions to examine.

Return Value

Type: System.Int32
The zero-based index position of value if that character is found, or -1 if it is not.


count or startIndex is negative.


startIndex is greater than the length of this string.


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

The search begins at startIndex and continues to startIndex + count -1. The character at startIndex + count is not included in the search.

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

This method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar values are the same. To perform a culture-sensitive search, use the CompareInfo.IndexOf method, where a Unicode scalar value representing a precomposed character, such as the ligature "Æ" (U+00C6), might be considered equivalent to any occurrence of the character's components in the correct sequence, such as "AE" (U+0041, U+0045), depending on the culture.

The following example demonstrates the IndexOf method.

' Example for the String.IndexOf( Char, Integer, Integer ) method. 
Imports System
Imports Microsoft.VisualBasic

Module IndexOfCII

    Sub Main()
        Dim br1 As String = _
            "0----+----1----+----2----+----3----+----" & _
        Dim br2 As String = _
            "0123456789012345678901234567890123456789" & _
        Dim str As String = _
            "ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi " & _
            "ABCDEFGHI abcdefghi ABCDEFGHI"

        Console.WriteLine( _
            "This example of String.IndexOf( Char, Integer, Integer )" & _
            vbCrLf & "generates the following output." )
        Console.WriteLine( _
            "{0}{1}{0}{2}{0}{3}{0}", _
            Environment.NewLine, br1, br2, str)

        FindAllChar("A"c, str)
        FindAllChar("a"c, str)
        FindAllChar("I"c, str)
        FindAllChar("i"c, str)
        FindAllChar("@"c, str)
        FindAllChar(" "c, str)
    End Sub 'Main

    Sub FindAllChar(target As Char, searched As String)

        Console.Write( _
            "The character ""{0}"" occurs at position(s): ", target)

        Dim startIndex As Integer = - 1
        Dim hitCount As Integer = 0

        ' Search for all occurrences of the target. 
        While True
            startIndex = searched.IndexOf( _
                target, startIndex + 1, _
                searched.Length - startIndex - 1)

            ' Exit the loop if the target is not found. 
            If startIndex < 0 Then 
                Exit While 
            End If 

            Console.Write("{0}, ", startIndex)
            hitCount += 1
        End While

        Console.WriteLine("occurrences: {0}", hitCount)

    End Sub 'FindAllChar
End Module 'IndexOfCII

' This example of String.IndexOf( Char, Integer, Integer ) 
' generates the following output. 
' 0----+----1----+----2----+----3----+----4----+----5----+----6----+----7 
' 01234567890123456789012345678901234567890123456789012345678901234567890 
' ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI 
' The character "A" occurs at position(s): 0, 20, 40, 60, occurrences: 4 
' The character "a" occurs at position(s): 10, 30, 50, occurrences: 3 
' The character "I" occurs at position(s): 8, 28, 48, 68, occurrences: 4 
' The character "i" occurs at position(s): 18, 38, 58, occurrences: 3 
' The character "@" occurs at position(s): occurrences: 0 
' The character " " occurs at position(s): 9, 19, 29, 39, 49, 59, occurrences: 6

.NET Framework

Supported in: 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 Silverlight 8.1, Windows Phone Silverlight 8

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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