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String.IndexOf Method (String, Int32, StringComparison)

Reports the zero-based index of the first occurrence of the specified string in the current String object. Parameters specify the starting search position in the current string and the type of search to use for the specified string.

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

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

Parameters

value
Type: System.String

The string to seek.

startIndex
Type: System.Int32

The search starting position.

comparisonType
Type: System.StringComparison

One of the enumeration values that specifies the rules for the search.

Return Value

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

ExceptionCondition
ArgumentNullException

value is Nothing.

ArgumentOutOfRangeException

startIndex is less than 0 (zero) or greater than the length of this string.

ArgumentException

comparisonType is not a valid System.StringComparison value.

Index numbering starts from 0. The startIndex parameter can range from 0 to the length of the string instance. If startIndex equals the length of the string instance, the method returns -1.

The comparisonType parameter specifies to search for the value parameter using the current or invariant culture, using a case-sensitive or case-insensitive search, and using word or ordinal comparison rules.

Notes to Callers

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 (that is, if comparisonType is not StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase), 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, StringComparison) method always returns startIndex, which is the character position at which the search begins.

In the following example, the IndexOf(String, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting with the third character position 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". The method returns the index of the soft hyphen in the first string only when it performs an ordinal comparison.

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, StringComparison.CurrentCulture))
      Console.WriteLine(s1.IndexOf(searchString, 2, StringComparison.Ordinal))
      Console.WriteLine(s2.IndexOf(searchString, 2, StringComparison.CurrentCulture))
      Console.WriteLine(s2.IndexOf(searchString, 2, StringComparison.Ordinal))
   End Sub 
End Module 
' The example displays the following output: 
'       4 
'       3 
'       3 
'       -1

The following example demonstrates three overloads of the IndexOf method that find the first occurrence of a string within another string using different values of the StringComparison enumeration.

' This code example demonstrates the  
' System.String.IndexOf(String, ..., StringComparison) methods. 

Imports System
Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim intro As String = "Find the first occurrence of a character using different " & _
                              "values of StringComparison." 
        Dim resultFmt As String = "Comparison: {0,-28} Location: {1,3}" 

        ' Define a string to search for. 
        ' U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE 
        Dim CapitalAWithRing As String = "Å" 

        ' Define a string to search.  
        ' The result of combining the characters LATIN SMALL LETTER A and COMBINING  
        ' RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character  
        ' LATIN SMALL LETTER A WITH RING ABOVE (U+00e5). 
        Dim cat As String = "A Cheshire c" & "å" & "t" 

        Dim loc As Integer = 0
        Dim scValues As StringComparison() =  { _
                        StringComparison.CurrentCulture, _
                        StringComparison.CurrentCultureIgnoreCase, _
                        StringComparison.InvariantCulture, _
                        StringComparison.InvariantCultureIgnoreCase, _
                        StringComparison.Ordinal, _
                        StringComparison.OrdinalIgnoreCase }
        Dim sc As StringComparison

        ' Clear the screen and display an introduction.
        Console.Clear()
        Console.WriteLine(intro)

        ' Display the current culture because culture affects the result. For example,  
        ' try this code example with the "sv-SE" (Swedish-Sweden) culture.
        Thread.CurrentThread.CurrentCulture = New CultureInfo("en-US")
        Console.WriteLine("The current culture is ""{0}"" - {1}.", _
                           Thread.CurrentThread.CurrentCulture.Name, _ 
                           Thread.CurrentThread.CurrentCulture.DisplayName)

        ' Display the string to search for and the string to search.
        Console.WriteLine("Search for the string ""{0}"" in the string ""{1}""", _
                           CapitalAWithRing, cat)
        Console.WriteLine()

        ' Note that in each of the following searches, we look for  
        ' LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains  
        ' LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates  
        ' the string was not found. 
        ' Search using different values of StringComparison. Specify the start  
        ' index and count.

        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc

        ' Search using different values of StringComparison. Specify the  
        ' start index. 

        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc

        ' Search using different values of StringComparison. 

        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc

    End Sub 'Main
End Class 'Sample


'Note: This code example was executed on a console whose user interface  
'culture is "en-US" (English-United States). 

'This code example produces the following results: 

'Find the first occurrence of a character using different values of StringComparison. 
'The current culture is "en-US" - English (United States). 
'Search for the string "Å" in the string "A Cheshire ca°t" 

'Part 1: Start index and count are specified. 
'Comparison: CurrentCulture               Location:  -1 
'Comparison: CurrentCultureIgnoreCase     Location:  12 
'Comparison: InvariantCulture             Location:  -1 
'Comparison: InvariantCultureIgnoreCase   Location:  12 
'Comparison: Ordinal                      Location:  -1 
'Comparison: OrdinalIgnoreCase            Location:  -1 

'Part 2: Start index is specified. 
'Comparison: CurrentCulture               Location:  -1 
'Comparison: CurrentCultureIgnoreCase     Location:  12 
'Comparison: InvariantCulture             Location:  -1 
'Comparison: InvariantCultureIgnoreCase   Location:  12 
'Comparison: Ordinal                      Location:  -1 
'Comparison: OrdinalIgnoreCase            Location:  -1 

'Part 3: Neither start index nor count is specified. 
'Comparison: CurrentCulture               Location:  -1 
'Comparison: CurrentCultureIgnoreCase     Location:  12 
'Comparison: InvariantCulture             Location:  -1 
'Comparison: InvariantCultureIgnoreCase   Location:  12 
'Comparison: Ordinal                      Location:  -1 
'Comparison: OrdinalIgnoreCase            Location:  -1 
'

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.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

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: 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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