Standard C Library Functions ctype(3C)
NAME
ctype, isalpha, isalnum, isascii, isblank, iscntrl, isdigit,
islower, isprint, isspace, isupper, ispunct, isgraph, isxdi-
git - character handling
SYNOPSIS
#include
int isalpha(int c);
int isalnum(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);
DESCRIPTION
These macros classify character-coded integer values. Each
is a predicate returning non-zero for true, 0 for false. The
behavior of these macros, except isascii(), is affected by
the current locale (see setlocale(3C)). To modify the
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Standard C Library Functions ctype(3C)
behavior, change the LCTYPE category in setlocale(), that
is, setlocale(LCTYPE, newlocale). In the "C" locale, or in
a locale where character type information is not defined,
characters are classified according to the rules of the US-
ASCI 7-bit coded character set.
The isascii() macro is defined on all integer values. The
rest are defined only where the argument is an int, the
value of which is representable as an unsigned char, or EOF,
which is defined by the header and represents
end-of-file.
Functions exist for all the macros defined below. To get the
function form, the macro name must be undefined (for exam-
ple, #undef isdigit).
For macros described with Default and Standard conforming
versions, standard-conforming behavior is provided for
standard-conforming applications (see standards(5)) and for
applications that define XPG4CHARCLAS before includ-
ing .
Default
isalpha() Tests for any character for which isupper() or
islower() is true.
Standard conforming
isalpha() Tests for any character for which isupper() or
islower() is true, or any character that is one
of the current locale-defined set of characters
for which none of iscntrl(), isdigit(),
ispunct(), or isspace() is true. In "C" locale,
isalpha() returns true only for the characters
for which isupper() or islower() is true.
isalnum() Tests for any character for which isalpha() or
isdigit() is true (letter or digit).
isascii() Tests for any ASCI character, code between 0
and 0177 inclusive.
isblank() Tests whether c is a character of class blank
in the current locale. This macro/function is
not available to applications conforming to
standards prior to SUSv3. See standards(5)
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Standard C Library Functions ctype(3C)
iscntrl() Tests for any ``control character'' as defined
by the character set.
isdigit() Tests for any decimal-digit character.
Default
isgraph() Tests for any character for which ispunct(),
isupper(), islower(), and isdigit() is true.
Standard conforming
isgraph() Tests for any character for which isalnum() and
ispunct() are true, or any character in the
current locale-defined "graph" class which is
neither a space ("") nor a character for which
iscntrl() is true.
islower() Tests for any character that is a lower-case
letter or is one of the current locale-defined
set of characters for which none of iscntrl(),
isdigit(), ispunct(), isspace(), or isupper()
is true. In the "C" locale, islower() returns
true only for the characters defined as lower-
case ASCI characters.
Default
isprint() Tests for any character for which ispunct(),
isupper(), islower(), isdigit(), and the space
character ("") is true.
Standard conforming
isprint() Tests for any character for which iscntrl() is
false, and isalnum(), isgraph(), ispunct(), the
space character (""), and the characters in the
current locale-defined "print" class are true.
ispunct() Tests for any printing character which is nei-
ther a space ("") nor a character for which
isalnum() or iscntrl() is true.
isspace() Tests for any space, tab, carriage-return, new-
line, vertical-tab or form-feed (standard
white-space characters) or for one of the
current locale-defined set of characters for
which isalnum() is false. In the "C" locale,
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Standard C Library Functions ctype(3C)
isspace() returns true only for the standard
white-space characters.
isupper() Tests for any character that is an upper-case
letter or is one of the current locale-defined
set of characters for which none of iscntrl(),
isdigit(), ispunct(), isspace(), or islower()
is true. In the "C" locale, isupper() returns
true only for the characters defined as upper-
case ASCI characters.
Default
isxdigit() Tests for any hexadecimal-digit character
([0-9], [A-F], or [a-f]).
Standard conforming
isxdigit() Tests for any hexadecimal-digit character
([0-9], [A-F], or [a-f] or the current
locale-defined sets of characters representing
the hexadecimal digits 10 to 15 inclusive). In
the "C" locale, only
0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f
are included.
RETURN VALUES
If the argument to any of the character handling macros is
not in the domain of the function, the result is undefined.
Otherwise, the macro or function returns non-zero if the
classification is TRUE and 0 if the classification is FALSE.
USAGE
These macros or functions can be used safely in mul-
tithreaded applications, as long as setlocale(3C) is not
being called to change the locale.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
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Standard C Library Functions ctype(3C)
ATRIBUTE TYPE ATRIBUTE VALUE
CSI Enabled
Interface Stability Standard
MT-Level MT-Safe with exceptions
SEE ALSO
setlocale(3C), stdio(3C), ascii(5), environ(5), standards(5)
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