String.IndexOf Method (String, Int32, StringComparison)

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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)

Syntax

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

public int IndexOf(
    string value,
    int startIndex,
    StringComparison comparisonType
)

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.

Exceptions

Exception	Condition
ArgumentNullException	value is nulla null reference (Nothing in Visual Basic).
ArgumentOutOfRangeException	startIndex is less than zero or greater than the length of this string.
ArgumentException	comparisonType is not a valid System.StringComparison value.

Remarks

Index numbering starts from zero. startIndex can range from 0 to one less than the length of the string instance.

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.

Platform Notes

 Silverlight for Windows Phone

The String.IndexOf method returns incorrect output when the string contains Unicode characters.

Examples

The following code 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.Threading
Imports System.Globalization

Class Example
   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      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

      ' Display an introduction.
      outputBlock.Text &= intro & vbCrLf

      ' 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")
      outputBlock.Text &= String.Format("The current culture is ""{0}"" - {1}.", _
                         Thread.CurrentThread.CurrentCulture.Name, _
                         Thread.CurrentThread.CurrentCulture.DisplayName) & vbCrLf

      ' Display the string to search for and the string to search.
      outputBlock.Text &= String.Format("Search for the string ""{0}"" in the string ""{1}""", _
                         CapitalAWithRing, cat) & vbCrLf
      outputBlock.Text &= vbCrLf

      ' 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.

      outputBlock.Text &= "Part 1: Start index and count are specified." & vbCrLf
      For Each sc In scValues
         loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc)
         outputBlock.Text &= String.Format(resultFmt, sc, loc) & vbCrLf
      Next sc

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

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

      ' Search using different values of StringComparison. 

      outputBlock.Text &= vbCrLf & "Part 3: Neither start index nor count is specified." & vbCrLf
      For Each sc In scValues
         loc = cat.IndexOf(CapitalAWithRing, sc)
         outputBlock.Text &= String.Format(resultFmt, sc, loc) & vbCrLf
      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
'

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

using System;
using System.Threading;
using System.Globalization;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string intro = "Find the first occurrence of a character using different " +
                     "values of StringComparison.";
      string resultFmt = "Comparison: {0,-28} Location: {1,3}";

      // Define a string to search for.
      // U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
      string CapitalAWithRing = "\u00c5";

      // 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).
      string cat = "A Cheshire c" + "\u0061\u030a" + "t";

      int loc = 0;
      StringComparison[] scValues = {
        StringComparison.CurrentCulture,
        StringComparison.CurrentCultureIgnoreCase,
        StringComparison.InvariantCulture,
        StringComparison.InvariantCultureIgnoreCase,
        StringComparison.Ordinal,
        StringComparison.OrdinalIgnoreCase };

      // Display an introduction.
      outputBlock.Text += intro + "\n";

      // 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");
      outputBlock.Text += String.Format("The current culture is \"{0}\" - {1}.",
                         Thread.CurrentThread.CurrentCulture.Name,
                         Thread.CurrentThread.CurrentCulture.DisplayName) + "\n";

      // Display the string to search for and the string to search.
      outputBlock.Text += String.Format("Search for the string \"{0}\" in the string \"{1}\"",
                         CapitalAWithRing, cat) + "\n";
      outputBlock.Text += "\n";

      // 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. 

      outputBlock.Text += "Part 1: Start index and count are specified." + "\n";
      foreach (StringComparison sc in scValues)
      {
         loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc);
         outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n";
      }

      // Search using different values of StringComparison. Specify the 
      // start index. 
      outputBlock.Text += "\nPart 2: Start index is specified." + "\n";
      foreach (StringComparison sc in scValues)
      {
         loc = cat.IndexOf(CapitalAWithRing, 0, sc);
         outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n";
      }

      // Search using different values of StringComparison. 
      outputBlock.Text += "\nPart 3: Neither start index nor count is specified." + "\n";
      foreach (StringComparison sc in scValues)
      {
         loc = cat.IndexOf(CapitalAWithRing, sc);
         outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n";
      }
   }
}

/*
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

*/

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

See Also

Reference

String Class

IndexOf Overload

System Namespace