411 REFERENCE · Wikibooks
A Little C Primer/C Character Class Test Library
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
These functions perform various tests on characters. They require the
declaration:
#include <ctype.h>
The character is represented as an "int" and the functions return an "int".
They return 0 if the test is false and non-0 if the test is true:
isalnum( c ) Character is alpha or digit.
isalpha( c ) Character is alpha.
iscntrl( c ) Character is control character.
isdigit( c ) Character is decimal digit.
isgraph( c ) Character is printing character (except space).
islower( c ) Character is lower-case.
isprint( c ) Character is printing character (including space).
ispunct( c ) Character is printing character but not space/alpha-digit.
isspace( c ) Character is space, FF, LF, CR, HT, VT.
isupper( c ) Character is upper-case.
isxdigit( c ) Character is hex digit.
The library also contains two conversion functions that also accept and
return an "int":
tolower( c ) Convert to lower case.
toupper( c ) Convert to upper case.