You use character sets in search, parsing, and comparison operations involving strings. Programmatic interfaces that require references to CFCharacterSet objects are currently under development in both Core Foundation and Carbon.
To obtain a CFCharacterSet object that can be passed into a function, you can either use one of the predefined character sets or create your own. To use one of the predefined sets--including such things as whitespace, alphanumeric characters, and decimal digits--call
CFCharacterSetGetPredefined
with one of the
CFCharacterSetPredefinedSet
constants. Several CFCharacterSet functions create character sets from strings and bitmapped data and others allow you to create mutable character sets. You can use a predefined character set as a starting point for building a custom set by making a mutable copy of it and changing that.
Because character sets often participate in performance-critical code, you should be aware of the aspects of their use that can affect the performance of your application. Mutable character sets are generally much more expensive than immutable character sets. They consume more memory and are costly to invert (an operation often performed in scanning a string). Because of this, you should follow these guidelines: