## page was renamed from Standard Library/B.02 Character Class Tests: <> == B.2 Character Class Tests: == The header declares functions for testing characters. For each function, the argument list is an int, whose value must be EOF or representable as an unsigned char, and the return value is an int. The functions return non-zero (true) if the argument c satisfies the condition described, and zero if not. {{{ isalnum(c) isalpha(c) or isdigit(c) is true isalpha(c) isupper(c) or islower(c) is true iscntrl(c) control character isdigit(c) decimal digit isgraph(c) printing character except space islower(c) lower-case letter isprint(c) printing character including space ispunct(c) printing character except space or letter or digit isspace(c) space, formfeed, newline, carriage return, tab, vertical tab isupper(c) upper-case letter isxdigit(c) hexadecimal digit }}} In the seven-bit ASCII character set, the printing characters are 0x20 (' ') to 0x7E ('-'); the control characters are 0 NUL to 0x1F (US), and 0x7F (DEL). In addition, there are two functions that convert the case of letters: {{{ int tolower(c) convert c to lower case int toupper(c) convert c to upper case }}} If c is an upper-case letter, tolower(c) returns the corresponding lower-case letter, toupper(c) returns the corresponding upper-case letter; otherwise it returns c.