Searches for the specified character and returns the zero-based index of the last occurrence within the section of the source string that extends from the beginning of the string to the specified index using the specified System.Globalization.CompareOptions value.
Syntax
Parameters
- source
- value
- startIndex
- options
Returns
The zero-based index of the last occurrence of value, if found, within the section of source that extends from the beginning of source to startIndex, using the specified comparison options; otherwise, -1. Returns startIndex if value is an ignorable character.
Remarks
The source string is searched backward starting at startIndex and ending at the beginning of the string.
The CompareOptions.StringSort value is not valid for this method.
If options does not include the CompareOptions.Ordinal value, this overload performs a culture-sensitive search. If the character is a Unicode value representing a precomposed character, such as the ligature "Æ" (U+00C6), it might be considered equivalent to any occurrence of its components in the correct sequence, such as "AE" (U+0041, U+0045), depending on the culture. If options includes the CompareOptions.Ordinal value, this overload performs an ordinal (culture-insensitive) search. A character is considered equivalent to another character only if the Unicode values are the same. Overloads of string.LastIndexOf(char) that search for a character perform an ordinal search, whereas those that search for a string perform a culture-sensitive search.
When possible, you should call string comparison methods that have a parameter of type System.Globalization.CompareOptions to specify the kind of comparison expected. As a general rule, use linguistic options (using the current culture) for comparing strings displayed in the user interface and specify CompareOptions.Ordinal or CompareOptions.OrdinalIgnoreCase for security comparisons.
Requirements
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0