This documentation is archived and is not being maintained.

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


Type: System.String
The string to seek.
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.


value is Nothing.


startIndex is negative.


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

Index numbering starts from zero. 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.

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

            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
                        Exit For
                    End If
                Next i

            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, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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