Manpages

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():

_XOPEN_SOURCE
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE

isblank():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

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 ('\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.

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.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Image /var/www/mancx/application/src/../www/___/img/man3/man3/isgraph1.png

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 standards require that the argument c for these functions is either EOF or a value that is representable in the type unsigned char. If the argument c is of type char, it must be cast to unsigned char, as in the following example:

char c;
...
res = toupper((unsigned char) c);

This is necessary because char may be the equivalent of signed char, in which case a byte where the top bit is set would be sign extended when converting to int, yielding a value that is outside the range of unsigned char.

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 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), toascii(3), tolower(3), toupper(3), uselocale(3), ascii(7), locale(7)

COLOPHON

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