isdigit, isdigit_l - test for a decimal digit
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.1-2017 defers to the ISO C standard.
The isdigit() [CX] and isdigit_l() functions shall test whether c is a character of class digit in the current locale, [CX] or in the locale represented by locale, respectively; see XBD Locale.
The c argument is an int, the value of which the application shall ensure is a character representable as an unsigned char 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.
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.
isalnum, isalpha, isblank, iscntrl, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit
XBD Locale, <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 , XSH/TC1-2008/0287 , and XSH/TC1-2008/0288  are applied.
return to top of page