String.IndexOf Method (String, Int32, 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, the number of characters in the current string to search, and the type of search to use for the specified string.
Assembly: mscorlib (in mscorlib.dll)
Public Function IndexOf ( value As String, startIndex As Integer, count As Integer, comparisonType As StringComparison ) As Integer
Parameters
- value
-
Type:
System.String
The string to seek.
- startIndex
-
Type:
System.Int32
The search starting position.
- count
-
Type:
System.Int32
The number of character positions to examine.
- comparisonType
-
Type:
System.StringComparison
One of the enumeration values that specifies the rules for the search.
Return Value
Type: System.Int32The zero-based index position of the value parameter from the start of the current instance if that string is found, or -1 if it is not. If value is Empty, the return value is startIndex.
| Exception | Condition |
|---|---|
| ArgumentNullException | value is null. |
| ArgumentOutOfRangeException | count or startIndex is negative. -or- startIndex is greater than the length of this instance. -or- count is greater than the length of this string minus startIndex. |
| ArgumentException | comparisonType is not a valid System.StringComparison value. |
Index numbering starts from 0 (zero). The startIndex parameter can range from 0 to the length of the string instance.
The search begins at startIndex and continues to startIndex + count -1. The character at startIndex + count is not included in the search.
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, Int32, StringComparison) method always returns startIndex, which is the character position at which the search begins.
In the following example, the IndexOf(String, Int32, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting in the third through sixth character positions 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. When it performs an ordinal comparison, however, it finds the substring only in the first 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" when it performs a culture-sensitive comparison. 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, 4, StringComparison.CurrentCulture)) Console.WriteLine(s1.IndexOf(searchString, 2, 4, StringComparison.Ordinal)) Console.WriteLine(s2.IndexOf(searchString, 2, 4, StringComparison.CurrentCulture)) Console.WriteLine(s2.IndexOf(searchString, 2, 4, StringComparison.Ordinal)) End Sub End Module ' The example displays the following output: ' 4 ' 3 ' 3 ' -1
The following exampledemonstrates 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 '
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1