Provided by: manpages-dev_5.10-1ubuntu1_all 
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).
┌─────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────┼───────────────┼─────────┤
│isalnum(), isalpha(), isascii(), │ Thread safety │ MT-Safe │
│isblank(), iscntrl(), isdigit(), │ │ │
│isgraph(), islower(), isprint(), │ │ │
│ispunct(), isspace(), isupper(), │ │ │
│isxdigit() │ │ │
└─────────────────────────────────┴───────────────┴─────────┘
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
This page is part of release 5.10 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 https://www.kernel.org/doc/man-pages/.