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.
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 upper case nor lower
case.
isascii()
checks whether c is a 7-bit
unsigned char
value that fits into
the ASCII character set. This function is a BSD extension
and is also an SVID extension.
isblank()
checks for a blank character; that is, a space or a tab.
This function is a GNU extension.
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 lower-case 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 a hexadecimal digits, i.e. 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 a zero value
if not.
CONFORMING TO
ANSI - C, BSD 4.3.
isascii() is a BSD extension
and is also an SVID extension.
isblank() is a GNU extension.
NOTE
The details of what characters belong into which class depend on the current
locale. For example,
isupper()
will not recognize an A - umlaut as an uppercase letter in the default
C
locale.