IndexOf Method (String, Int32, StringComparison)

String.IndexOf Method (String, 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 and the type of search to use for the specified string.

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

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


Type: System.String

The string to seek.

Type: System.Int32

The search starting position.

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 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

value is null.


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


comparisonType is not a valid System.StringComparison value.

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.

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, theIndexOf(String, Int32, StringComparison) method always returns startIndex, which is the character position at which the search begins.

In the following example, the IndexOf(String, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting with the third character position 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. 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". The method returns the index of the soft hyphen in the first string only when it performs an ordinal comparison.

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

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.

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

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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