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)
member IndexOf : value:string * startIndex:int * count:int * comparisonType:StringComparison -> int
- Type: System.String
The string to seek.
- Type: System.Int32
The search starting position.
- Type: System.Int32
The number of character positions to examine.
- Type: System.StringComparison
One of the enumeration values that specifies the rules for the search.
value is a null reference (Nothing in Visual Basic).
count or startIndex is negative.
startIndex is greater than the length of this instance.
count is greater than the length of this string minus startIndex.
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 method always returns startIndex, which is the character position at which the search begins.
In the following example, the 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.