IndexOf Method (Char, Int32, Int32)

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)

'Declaration
Public Function IndexOf ( _
	value As Char, _
	startIndex As Integer, _
	count As Integer _
) As Integer
'Usage
Dim instance As String 
Dim value As Char 
Dim startIndex As Integer 
Dim count As Integer 
Dim returnValue As Integer 

returnValue = instance.IndexOf(value, _
	startIndex, count)

Parameters

value
Type: System.Char

A Unicode character 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 character is found, or -1 if it is not.

ExceptionCondition
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.

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.

The search for value is case-sensitive.

This method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar value 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----+----" & _
            "4----+----5----+----6----+----7" 
        Dim br2 As String = _
            "0123456789012345678901234567890123456789" & _
            "0123456789012345678901234567890" 
        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

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

Clarified the relationship between string length and the startIndex parameter.

Content bug fix.

Noted that an exception is not thrown for an empty string if the index parameter is invalid.

Content bug fix.

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