The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


isdigit - test for a decimal digit


#include <ctype.h>

int isdigit(int c);


The isdigit() function tests whether c is a character of class digit in the program's current locale, see the XBD specification, Locale .

In all cases c is an int, the value of which must be a character representable as an unsigned char or must equal the value of the macro EOF. If the argument has any other value, the behaviour is undefined.


The isdigit() function returns non-zero if c is a decimal digit; otherwise it returns 0.


No errors are defined.




To ensure applications portability, especially across natural languages, only this function and those listed in the SEE ALSO section should be used for character classification.




isalnum(), isalpha(), iscntrl(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit(), <ctype.h>.


Derived from Issue 1 of the SVID.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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