ISALPHA(3) Linux Programmer's Manual ISALPHA(3)NAME
isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower,
isprint, ispunct, isspace, isupper, isxdigit, isalnum_l, isalpha_l,
isascii_l, isblank_l, iscntrl_l, isdigit_l, isgraph_l, islower_l,
isprint_l, ispunct_l, isspace_l, isupper_l, isxdigit_l - character
classification functions
SYNOPSIS
#include <ctype.h>
int isalnum(int c);
int isalpha(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);
int isascii(int c);
int isblank(int c);
int isalnum_l(int c, locale_t locale);
int isalpha_l(int c, locale_t locale);
int isblank_l(int c, locale_t locale);
int iscntrl_l(int c, locale_t locale);
int isdigit_l(int c, locale_t locale);
int isgraph_l(int c, locale_t locale);
int islower_l(int c, locale_t locale);
int isprint_l(int c, locale_t locale);
int ispunct_l(int c, locale_t locale);
int isspace_l(int c, locale_t locale);
int isupper_l(int c, locale_t locale);
int isxdigit_l(int c, locale_t locale);
int isascii_l(int c, locale_t locale);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
isascii():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
isblank():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
isalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(),
isgraph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(), isup‐
per_l(), isxdigit_l():
Since glibc 2.10:
_XOPEN_SOURCE >= 700
Before glibc 2.10:
_GNU_SOURCE
isascii_l():
Since glibc 2.10:
_XOPEN_SOURCE >= 700 && (_SVID_SOURCE || _BSD_SOURCE)
Before glibc 2.10:
_GNU_SOURCE
DESCRIPTION
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 specified locale. The functions without the "_l" suffix perform
the check based on the current locale.
The functions with the "_l" suffix perform the check based on the
locale specified by the locale object locale. The behavior of these
functions is undefined if locale is the special locale object
LC_GLOBAL_LOCALE (see duplocale(3)) or is not a valid locale object
handle.
The list below explains the operation of the functions without the "_l"
suffix; the functions with the "_l" suffix differ only in using the
locale object locale instead of the current locale.
isalnum()
checks for an alphanumeric character; it is equivalent to (isal‐
pha(c) || isdigit(c)).
isalpha()
checks for an alphabetic character; in the standard "C" 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 uppercase nor lowercase.
isascii()
checks whether c is a 7-bit unsigned char value that fits into
the ASCII character set.
isblank()
checks for a blank character; that is, a space or a tab.
iscntrl()
checks for a control character.
isdigit()
checks for a digit (0 through 9).
isgraph()
checks for any printable character except space.
islower()
checks for a lowercase character.
isprint()
checks for any printable character including space.
ispunct()
checks for any printable character which is not a space or an
alphanumeric character.
isspace()
checks for white-space characters. In the "C" and "POSIX"
locales, these are: space, form-feed ('\f'), newline ('\n'),
carriage return ('\r'), horizontal tab ('\t'), and vertical tab
('\v').
isupper()
checks for an uppercase letter.
isxdigit()
checks for hexadecimal digits, that is, one of
0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.
RETURN VALUE
The values returned are nonzero if the character c falls into the
tested class, and zero if not.
ATTRIBUTES
Multithreading (see pthreads(7))
The isalnum(), isalpha(), isascii(), isblank(), iscntrl(), isdigit(),
isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), and
isxdigit() functions are thread-safe.
VERSIONSisalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(),
isgraph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(), isup‐
per_l(), isxdigit_l(), and isascii_l() are available since glibc 2.3.
CONFORMING TO
C89 specifies isalnum(), isalpha(), iscntrl(), isdigit(), isgraph(),
islower(), isprint(), ispunct(), isspace(), isupper(), and isxdigit(),
but not isascii() and isblank(). POSIX.1-2001 also specifies those
functions, and also isascii() (as an XSI extension) and isblank(). C99
specifies all of the preceding functions, except isascii().
POSIX.1-2008 marks isascii() as obsolete, noting that it cannot be used
portably in a localized application.
POSIX.1-2008 specifies isalnum_l(), isalpha_l(), isblank_l(), iscn‐
trl_l(), isdigit_l(), isgraph_l(), islower_l(), isprint_l(),
ispunct_l(), isspace_l(), isupper_l(), and isxdigit_l().
isascii_l() is a GNU extension.
NOTES
The details of what characters belong to which class depend on the
locale. For example, isupper() will not recognize an A-umlaut (Ä) as
an uppercase letter in the default C locale.
SEE ALSOiswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3), iswdigit(3), isw‐
graph(3), iswlower(3), iswprint(3), iswpunct(3), iswspace(3), iswup‐
per(3), iswxdigit(3), newlocale(3), setlocale(3), uselocale(3),
toascii(3), tolower(3), toupper(3), ascii(7), locale(7)COLOPHON
This page is part of release 3.65 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2014-03-18 ISALPHA(3)
