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.NET Framework Class Library

String.IndexOf Method (String, 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.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
Public Function IndexOf ( _
	value As String, _
	startIndex As Integer _
) As Integer

Parameters

value
Type: System.String

The string to seek.

startIndex
Type: System.Int32

The search starting position.

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.
Exception Condition
ArgumentNullException

value is null.

ArgumentOutOfRangeException

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

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.

This method performs a word (case-sensitive and culture-sensitive) search using the current culture. The search begins at the startIndex character position of this instance and continues until the last character position.

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) method always returns startIndex, which is the character position at which the search begins. In the following example, the IndexOf(String, Int32) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" 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. 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))
      Console.WriteLine(s2.IndexOf(searchString, 2))
   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 find the first index of a substring that occurs after a particular character position by using the comparison rules of the current culture, call the IndexOf(String, Int32, StringComparison) method overload with a value of StringComparison.CurrentCulture for its comparisonType parameter.

The following example searches for all occurrences of a specified string within a target string.

Imports System

Public Class IndexOfTest

    Public Shared Sub Main()
        Dim strSource As String = "This is the string which we will perform the search on"

        Console.WriteLine("The search string is:{0}{1}{0}", Environment.NewLine, strSource)
        Dim strTarget As String = "" 
        Dim found As Integer = 0
        Dim totFinds As Integer = 0

        Do
            Console.Write("Please enter a search value to look for in the above string (hit Enter to exit) ==> ")

            strTarget = Console.ReadLine()
            If strTarget <> "" Then 
                Dim i As Integer 


                For i = 0 To strSource.Length - 1

                    found = strSource.IndexOf(strTarget, i)
                    If found >= 0 Then

                        totFinds += 1
                        i = found
                    Else 
                        Exit For 
                    End If 
                Next i
            Else 
                Return 

            End If
            Console.WriteLine("{0}The search parameter '{1}' was found {2} times.{0}", Environment.NewLine, strTarget, totFinds)

            totFinds = 0

        Loop While True 
    End Sub 'Main
End Class 'IndexOfTest

.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.