String.LastIndexOf Method (String, Int32, Int32, StringComparison)
Reports the zero-based index position of the last occurrence of a specified string within this instance. The search starts at a specified character position and proceeds backward toward the beginning of the string for the specified number of character positions. A parameter specifies the type of comparison to perform when searching for the specified string.
Assembly: mscorlib (in mscorlib.dll)
member LastIndexOf : value:string * startIndex:int * count:int * comparisonType:StringComparison -> int
- Type: System.String
The string to seek.
- Type: System.Int32
The search starting position. The search proceeds from startIndex toward the beginning of this instance.
- 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 is negative.
The current instance does not equal String.Empty, and startIndex is negative.
The current instance does not equal String.Empty, and startIndex is greater than the length of this instance.
The current instance does not equal String.Empty, and startIndex + 1 - count specifies a position that is not within this instance.
The current instance equals String.Empty and start is less than -1 or greater than zero.
The current instance equals String.Empty and count is greater than 1.
comparisonType is not a valid System.StringComparison value.
Index numbering starts from zero. That is, the first character in the string is at index zero and the last is at Length - 1.
The search begins at the startIndex character position and proceeds backward until either value is found or count character positions have been examined. For example, if startIndex is Length - 1, the method searches backward count characters from the last character in the string.
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" in all but the first character position before the final "m" in two strings. Only one of the strings contains the required substring. 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.