isprint, ispunct, isspace, isupper, isxdigit - character classification
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)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
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.
checks for an alphanumeric character; it is equivalent to (isal-
pha(c) || isdigit(c)).
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.
checks whether c is a 7-bit unsigned char value that fits into
the ASCII character set.
checks for a blank character; that is, a space or a tab.
checks for a control character.
checks for any printable character which is not a space or an
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
checks for an uppercase letter.
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.
The values returned are nonzero if the character c falls into the
tested class, and a zero value if not.
C99, 4.3BSD. C89 specifies all of these functions except isascii() and
isblank(). isascii() is a BSD extension and is also an SVr4 extension.
isblank() conforms to POSIX.1-2001 and C99 22.214.171.124. POSIX.1-2008 marks
isascii() as obsolete, noting that it cannot be used portably in a
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.
iswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3), iswdigit(3), isw-
graph(3), iswlower(3), iswprint(3), iswpunct(3), iswspace(3), iswup-
per(3), iswxdigit(3), setlocale(3), toascii(3), tolower(3), toupper(3),
This page is part of release 3.35 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://man7.org/linux/man-pages/.
GNU 2010-09-20 ISALPHA(3)
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