ISDIGIT(3) Library Functions Manual ISDIGIT(3)

isdigit isdigit_l — test for a decimal digit

#include <ctype.h>

int isdigit(int c);
[CX] int isdigit_l(int c, locale_t locale);

For isdigit (): [CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard.

The isdigit () [CX] and isdigit_l () functions shall test whether c is a character of class in the current locale, [CX] or in the locale represented by locale, respectively; see XBD V1_chap07(7).

The c argument is an , the value of which the application shall ensure is a character representable as an or equal to the value of the macro EOF. If the argument has any other value, the behavior is undefined.

[CX] The behavior is undefined if the locale argument to isdigit_l () is the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle.

The isdigit () [CX] and isdigit_l () functions shall return non-zero if c is a decimal digit; otherwise, they shall return 0.

No errors are defined.

None.

To ensure applications portability, especially across natural languages, only these functions and the functions in the reference pages listed in the SEE ALSO section should be used for character classification.

None.

None.

isalnum(3), isalpha(3), isblank(3), iscntrl(3), isgraph(3), islower(3), isprint(3), ispunct(3), isspace(3), isupper(3), isxdigit(3)

XBD V1_chap07(7), <ctype.h>, <locale.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The normative text is updated to avoid use of the term "must" for application requirements.

The isdigit_l () function is added from The Open Group Technical Standard, 2006, Extended API Set Part 4.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0286 [302], XSH/TC1-2008/0287 [283], and XSH/TC1-2008/0288 [283] are applied.

June 14, 2024 posix.fail