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PROLOG
       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.


NAME
       isdigit, isdigit_l — test for a decimal digit


SYNOPSIS
       #include <ctype.h>

       int isdigit(int c);
       int isdigit_l(int c, locale_t locale);


DESCRIPTION
       For  isdigit():  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() and isdigit_l() functions shall test whether c is a character of class digit
       in the current locale, or in the locale represented by locale, respectively; see the  Base
       Definitions volume of POSIX.1‐2017, Chapter 7, 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.

       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.


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


ERRORS
       No errors are defined.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       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.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


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

       The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale, <ctype.h>, <locale.h>


COPYRIGHT
       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  by
       the  Institute  of  Electrical  and Electronics Engineers, Inc and The Open Group.  In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .