character handling routines
. . .
The character classification macros listed below
are defined by the <ctype.h> header file.
They each return nonzero for true, zero for false.
These functions classify character-coded integer values
according to the rules of the coded character set
defined by character type information in the program's locale
In the C locale, or in a locale where character type information
is not defined, characters are classified according to
the rules of the US-ASCII 7-bit coded character set,
returning zero for values above octal 0177.
In all cases the argument is an integer, the value of which
must be representable as an unsigned char
or must equal the value of the macro EOF.
If the argument has any other value, the behavior is undefined.
isascii is defined on all integer values.
tests for the digits 0 through 9.
tests for any character for which isdigit is true or for
the letters a through f or A through F.
tests for any lowercase letter as defined by the character set.
tests for any uppercase letter as defined by the character set.
tests for any character for which islower or isupper
is true and possibly any others as defined by the character set.
tests for any character for which isalpha or isdigit
tests for a space, horizontal-tab, carriage return, newline,
vertical-tab, or form-feed.
tests for ``control characters'' as defined by the character set.
tests for any character other than the ones for which isalnum,
iscntrl, or isspace is true.
tests for a space or any character for which isalnum
or ispunct is true
or other ``printing character'' as defined by the character set.
tests for any character for which isprint is true,
except for space.
tests for an ASCII character
(a non-negative number less than 0200).
All the character classification macros
do a table lookup.
If the argument to any of the character handling macros
is not in the domain of the function, the result is undefined.
If a character variable or constant is passed
to these functions or macros,
undefined results may occur on machines which sign-extend
characters by default.
isalnum, isalpha, iscntrl, isdigit,
isgraph, islower, isprint, ispunct,
isspace, isupper, and isxdigit
are conformant with:
X/Open Portability Guide, Issue 3, 1989
ANSI X3.159-1989 Programming Language -- C
IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C Language] (ISO/IEC 9945-1)
NIST FIPS 151-1
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