Standard wide character classification subroutines

The isw* subroutines determine various aspects of a standard wide character classification. The isw* subroutines also work with single-byte code sets. Use the isw* subroutines in preference to the wctype and iswctype subroutines. Use the wctype and iswctype subroutines only for extended character class properties (for example, Japanese language properties).

When using the wide character functions to convert the case in several blocks of data, the application must convert characters from multibyte to wide character code form. Because this can affect performance in single-byte code set locales, consider providing two conversion paths in your application. The traditional path for single-byte code set locales would convert case using the isupper,islower, toupper, and tolower subroutines. The alternate path for multibyte code set locales would convert multibyte characters to wide character code form and convert case using the iswupper, iswlower, towupper and towlower subroutines. When converting multibyte characters to wide character code form, an application needs to handle special cases where a multibyte character may split across successive blocks.