isalnum(), isalpha(), iscntrl(), isdigit(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), and isxdigit()

Syntax

  #include <ctype.h>

  int isalnum (int ch);

  int isalpha (int ch);

...

  int isxdigit(int ch);

Description

These functions determine whether character ch belongs to a certain set of characters. The following table describes the character ranges tested by the functions.

Table 1. Appropriate character range for the testing functions
Function	Range Tested
`isalnum()`	alphanumeric character, i.e., `A-Z`, `a-z` or `0-9.`
`isalpha()`	an alphabetic character, i.e., `A-Z` or `a-z.`
`iscntrl()`	a control character, i.e., `\000-\037` or `\177` ( `DEL`).
`isdigit()`	a decimal digit, i.e., `0-9`.
`isgraph()`	a printable character except space ( `! - or ~` ).
`islower()`	a lower case letter, i.e., `a-z`.
`isprint()`	a printable character ( `' '-'~'`).
`ispunct()`	a punctuation character, i.e., `'!'-'/'`, `':'-'@'`, `'['-'''` and `'{'-'~'`.
`isspace()`	a white space character, i.e., `' '`, `'\f'`, `'\n'`, `'\r'`, `'\t'` and `'\v'`.
`isupper()`	an upper case letter, i.e., `A-Z`.
`isxdigit()`	a hexadecimal digit, i.e., `0-9`, `A-F` or `a-f`.

Return

TRUE (i.e., 1), if ch is in the character class; zero otherwise.

See also

tolower() and

toupper()