ISALPHA(3) Linux Programmer's Manual ISALPHA(3)
NAME
isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit - character classifi-
cation 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 (isalpha(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 ('
'), carriage
return ('
'), horizontal tab (' '), 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.
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 exten-
sion. 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
(A) as an uppercase letter in the default C locale.
SEE ALSO
iswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3), iswdigit(3), iswgraph(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 3.27 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
2010-09-20 ISALPHA(3)
