ISALPHA(3) Linux Programmer's Manual ISALPHA(3)NAME
isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower,
isprint, ispunct, isspace, isupper, isxdigit - character classification
routines
SYNOPSIS
#include <ctype.h>
int isalnum(int c);
int isalpha(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);
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
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 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 upper case nor lower case.
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 lower-case 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 a 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 a zero value 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.
CONFORMING TO
C99, 4.3BSD. C89 specifies all of these functions except isascii() and
isblank(). isascii() is a BSD extension and is also an SVr4 extension.
isblank() conforms to POSIX.1-2001 and C99 7.4.1.3. POSIX.1-2008 marks
isascii() as obsolete, noting that it cannot be used portably in a
localized application.
NOTES
The details of what characters belong into which class depend on the
current 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), setlocale(3), toascii(3), tolower(3), toupper(3),
ascii(7), locale(7)COLOPHON
This page is part of release 3.58 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 2014-01-27 ISALPHA(3)
