Provided by: manpages-dev_6.8-2_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
LIBRARY
Standard C library (libc, -lc)
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 >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE
isblank():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
salnum_l(), salpha_l(), sblank_l(), scntrl_l(), sdigit_l(), sgraph_l(), slower_l(),
sprint_l(), spunct_l(), sspace_l(), supper_l(), sxdigit_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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌───────────────────────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├───────────────────────────────────────────────────────────────┼───────────────┼─────────┤
│isalnum(), isalpha(), isascii(), isblank(), iscntrl(), │ Thread safety │ MT-Safe │
│isdigit(), isgraph(), islower(), isprint(), ispunct(), │ │ │
│isspace(), isupper(), isxdigit() │ │ │
└───────────────────────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
isalnum()
isalpha()
iscntrl()
isdigit()
isgraph()
islower()
isprint()
ispunct()
isspace()
isupper()
isxdigit()
isblank()
C11, POSIX.1-2008.
isascii()
isalnum_l()
isalpha_l()
isblank_l()
iscntrl_l()
isdigit_l()
isgraph_l()
islower_l()
isprint_l()
ispunct_l()
isspace_l()
isupper_l()
isxdigit_l()
POSIX.1-2008.
isascii_l()
GNU.
HISTORY
isalnum()
isalpha()
iscntrl()
isdigit()
isgraph()
islower()
isprint()
ispunct()
isspace()
isupper()
isxdigit()
C89, POSIX.1-2001.
isblank()
C99, POSIX.1-2001.
isascii()
POSIX.1-2001 (XSI).
POSIX.1-2008 marks it as obsolete, noting that it cannot be used portably in a
localized application.
isalnum_l()
isalpha_l()
isblank_l()
iscntrl_l()
isdigit_l()
isgraph_l()
islower_l()
isprint_l()
ispunct_l()
isspace_l()
isupper_l()
isxdigit_l()
glibc 2.3. POSIX.1-2008.
isascii_l()
glibc 2.3.
CAVEATS
The standards require that the argument c for these functions is either EOF or a value
that is representable in the type unsigned char; otherwise, the behavior is undefined. 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)