ctype(3C) Standard C Library Functions ctype(3C)NAME
ctype, isalpha, isalnum, isascii, isblank, iscntrl, isdigit, islower,
isprint, isspace, isupper, ispunct, isgraph, isxdigit - character han‐
dling
SYNOPSIS
#include <ctype.h>
int isalpha(int c);
int isalnum(int c);
int isascii(int c);
int isblank(int c);
int iscntrl(int c);
int isdigit(int c);
int isgraph(int c);
int islower(int c);
int isprint(int c);
int ispunct(int c);
int isspace(int c);
int isupper(int c);
int isxdigit(int c);
DESCRIPTION
These macros classify character-coded integer values. Each is a predi‐
cate returning non-zero for true, 0 for false. The behavior of these
macros, except isascii(), is affected by the current locale (see setlo‐
cale(3C)). To modify the behavior, change the LC_TYPE category in set‐
locale(), that is, setlocale(LC_CTYPE, newlocale). In the "C" locale,
or in a locale where character type information is not defined, charac‐
ters are classified according to the rules of the US-ASCII 7-bit coded
character set.
The isascii() macro is defined on all integer values. The rest are
defined only where the argument is an int, the value of which is repre‐
sentable as an unsigned char, or EOF, which is defined by the <stdio.h>
header and represents end-of-file.
Functions exist for all the macros defined below. To get the function
form, the macro name must be undefined (for example, #undef isdigit).
For macros described with Default and Standard conforming versions,
standard-conforming behavior is provided for standard-conforming appli‐
cations (see standards(5)) and for applications that define
__XPG4_CHAR_CLASS__ before including <ctype.h>.
Default
isalpha() Tests for any character for which isupper() or
islower() is true.
Standard conforming
isalpha() Tests for any character for which isupper() or
islower() is true, or any character that is one of the
current locale-defined set of characters for which none
of iscntrl(), isdigit(), ispunct(), or isspace() is
true. In "C" locale, isalpha() returns true only for
the characters for which isupper() or islower() is
true.
isalnum() Tests for any character for which isalpha() or
isdigit() is true (letter or digit).
isascii() Tests for any ASCII character, code between 0 and 0177
inclusive.
isblank() Tests whether c is a character of class blank in the
current locale. This macro/function is not available to
applications conforming to standards prior to SUSv3.
See standards(5)iscntrl() Tests for any ``control character'' as defined by the
character set.
isdigit() Tests for any decimal-digit character.
Default
isgraph() Tests for any character for which ispunct(), isupper(),
islower(), and isdigit() is true.
Standard conforming
isgraph() Tests for any character for which isalnum() and
ispunct() are true, or any character in the current
locale-defined "graph" class which is neither a space
("") nor a character for which iscntrl() is true.
islower() Tests for any character that is a lower-case letter or
is one of the current locale-defined set of characters
for which none of iscntrl(), isdigit(), ispunct(), iss‐
pace(), or isupper() is true. In the "C" locale,
islower() returns true only for the characters defined
as lower-case ASCII characters.
Default
isprint() Tests for any character for which ispunct(), isupper(),
islower(), isdigit(), and the space character ("") is
true.
Standard conforming
isprint() Tests for any character for which iscntrl() is false,
and isalnum(), isgraph(), ispunct(), the space charac‐
ter (""), and the characters in the current locale-
defined "print" class are true.
ispunct() Tests for any printing character which is neither a
space ("") nor a character for which isalnum() or iscn‐
trl() is true.
isspace() Tests for any space, tab, carriage-return, newline,
vertical-tab or form-feed (standard white-space charac‐
ters) or for one of the current locale-defined set of
characters for which isalnum() is false. In the "C"
locale, isspace() returns true only for the standard
white-space characters.
isupper() Tests for any character that is an upper-case letter or
is one of the current locale-defined set of characters
for which none of iscntrl(), isdigit(), ispunct(), iss‐
pace(), or islower() is true. In the "C" locale, isup‐
per() returns true only for the characters defined as
upper-case ASCII characters.
Default
isxdigit() Tests for any hexadecimal-digit character ([0−9],
[A−F], or [a−f]).
Standard conforming
isxdigit() Tests for any hexadecimal-digit character ([0−9],
[A−F], or [a−f] or the current locale-defined sets of
characters representing the hexadecimal digits 10 to 15
inclusive). In the "C" locale, only
0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f
are included.
RETURN VALUES
If the argument to any of the character handling macros is not in the
domain of the function, the result is undefined. Otherwise, the macro
or function returns non-zero if the classification is TRUE and 0 if the
classification is FALSE.
USAGE
These macros or functions can be used safely in multithreaded applica‐
tions, as long as setlocale(3C) is not being called to change the
locale.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│CSI │Enabled │
│Interface Stability │Standard │
│MT-Level │MT-Safe with exceptions │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOsetlocale(3C), stdio(3C), ascii(5), environ(5), standards(5)SunOS 5.10 28 Jan 2005 ctype(3C)
