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String.IndexOf Method (String, StringComparison)

Reports the zero-based index of the first occurrence of the specified string in the current String object. A parameter specifies the type of search to use for the specified string.

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

member IndexOf : 
        value:string * 
        comparisonType:StringComparison -> int

Parameters

value
Type: System.String

The string to seek.

comparisonType
Type: System.StringComparison

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

Return Value

Type: System.Int32
The 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 0.

ExceptionCondition
ArgumentNullException

value is a null reference (Nothing in Visual Basic).

ArgumentException

comparisonType is not a valid System.StringComparison value.

Index numbering starts from zero.

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, StringComparison) method always returns 0 (zero) to indicate that the match is found at the beginning of the current instance.

In the following example, the IndexOf(String, StringComparison) method is used to find three substrings (a soft hyphen (U+00AD), a soft hyphen followed by "n", and a soft hyphen followed by "m") in two strings. Only one of the strings contains a soft hyphen. If the example is run on the .NET Framework 4 or later, because the soft hyphen is an ignorable character, a culture-sensitive search returns the same value that it would return if the soft hyphen were not included in the search string. An ordinal search, however, successfully finds the soft hyphen in one string and reports that it is absent from the second string.

No code example is currently available or this language may not be supported.

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.

No code example is currently available or this language may not be supported.

.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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