Character Handling - The GNU C Library

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## 4 Character Handling

Programs that work with characters and strings often need to classify a character—is it alphabetic, is it a digit, is it whitespace, and so on—and perform case conversion operations on characters. The functions in the header file `ctype.h` are provided for this purpose. Since the choice of locale and character set can alter the classifications of particular character codes, all of these functions are affected by the current locale. (More precisely, they are affected by the locale currently selected for character classification—the `LC_CTYPE` category; see Locale Categories.)

The ISO C standard specifies two different sets of functions. The one set works on `char` type characters, the other one on `wchar_t` wide characters (see Extended Char Intro).