ISDIGIT(3) Library Functions Manual ISDIGIT(3)

isdigit, isnumber — decimal-digit character test

Standard C Library (libc, -lc)

#include <ctype.h>

int
isdigit(int c);

int
isnumber(int c);

The () function tests for a decimal digit character. Regardless of locale, this includes the following characters only:

``0''``1''``2''``3''``4''
``5''``6''``7''``8''``9''

The () function behaves similarly to isdigit(), but may recognize additional characters, depending on the current locale setting.

The value of the argument must be representable as an unsigned char or the value of EOF.

The isdigit() and isnumber() functions return zero if the character tests false and return non-zero if the character tests true.

The 4.4BSD extension of accepting arguments outside of the range of the unsigned char type in locales with large character sets is considered obsolete and may not be supported in future releases. The iswdigit() function should be used instead.

ctype(3), isalnum_l(3), iswdigit(3), multibyte(3), ascii(7)

The isdigit() function conforms to ISO/IEC 9899:1990 (“ISO C90”).

The isnumber() function appeared in 4.4BSD.

May 4, 2007 macOS 15.2