Parameters

source

The string to search.

value

The string to locate within source.

startIndex

The zero-based starting index of the backward search.

options

A value that defines how source and value should be compared. options is either the enumeration value CompareOptions.Ordinal, or a bitwise combination of one or more of the following values: CompareOptions.IgnoreCase, CompareOptions.IgnoreSymbols, CompareOptions.IgnoreNonSpace, CompareOptions.IgnoreWidth, and CompareOptions.IgnoreKanaType.

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. A Unicode value representing a precomposed character, such as the ligature "Æ" (U+00C6), might be considered equivalent to any occurrence of the character's 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, where the Unicode values are compared.

Note:

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