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The header <ctype.h>
declares functions for
testing characters. For each function, the argument is an
int
, whose value must be EOF or representable as an unsigned
char
, and the return value is an int
. The
functions return non-zero (true) if the argument c
satisfies the condition described, and zero if not.
isalnum(c) |
isalpha(c) or isdigit(c) is true |
|
isalpha(c) |
isupper(c) or islower(c) is true |
|
iscntrl(c) |
control character | |
isdigit(c) |
decimal digit | |
isgraph(c) |
printing character except space | |
islower(c) |
lower-case letter | |
isprint(c) |
printing character including space | |
ispunct(c) |
printing character except space or letter or digit | |
isspace(c) |
space, formfeed, newline, carriage return, tab, vertical tab | |
isupper(c) |
upper-case letter | |
isxdigit(c) |
hexadecimal digit |
In the seven-bit ASCII character set, the printing characters are
0x20
(' '
) to 0x7E
('~'
); the control characters are 0
(NUL
) to 0x1F
(US
), and
0x7F
(DEL
).
In addition, there are two functions that convert the case of letters:
int tolower(int c) |
convert c to lower case
| |
int toupper(int c) |
convert c to upper case
|
If c
is an upper-case letter, tolower(c)
returns the corresponding lower-case letter; otherwise it returns
c
. If c
is a lower-case letter,
toupper(c)
returns the corresponding upper-case letter;
otherwise it returns c
.
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Last modified: Mon Mar 27 13:03:35 2000