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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(), isupper_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 (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 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 (aq\faq), newline (aq\naq), carriage return (aq\raq), horizontal tab (aq\taq), and vertical tab (aq\vaq).
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.

Versions

isalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(), isgraph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(), isupper_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(), iscntrl_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 (: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) , iswupper(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 3.78 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.

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