These functions check whether c, which must have the value of an unsigned char or EOF, falls into a certain character class according to the current locale.
checks for an alphanumeric character; it is equivalent to (isalpha(c) || isdigit(c)).
checks for an alphabetic character; in the standard locale, it is equivalent to (isupper(c) || islower(c)). In some locales, there may be additional characters for which isalpha() is true--letters which are neither upper case nor lower case.
checks whether c is a 7-bit unsigned char value that fits into the ASCII character set. This function is a BSD extension and is also an SVID extension.
checks for a blank character; that is, a space or a tab. This function is a GNU extension.
checks for a control character.
checks for a digit (0 through 9).
checks for any printable character except space.
checks for a lower-case character.
checks for any printable character including space.
checks for any printable character which is not a space or an alphanumeric character.
checks for white-space characters. In the and locales, these are: space, form-feed ('f'), newline ('n'), carriage return ('r'), horizontal tab ('t'), and vertical tab ('v').
checks for an uppercase letter.