This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       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 .

IEEE/The Open Group                                   2017                                       ISALPHA(3POSIX)

       For isalpha(): 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 isalpha() and isalpha_l() functions shall test whether c is a character of class alpha in the current
       locale, or in the locale represented  by  locale,  respectively;  see  the  Base  Definitions  volume  of
       POSIX.1‐2017, Chapter7, Locale.

       The c argument is an int, the value of which the application shall ensure is representable as an unsignedchar  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  isalpha_l()  is  the  special  locale  object
       LC_GLOBAL_LOCALE or is not a valid locale object handle.

       No errors are defined.

       Thefollowingsectionsareinformative.

       None.

       None.

       isalpha, isalpha_l — test for an alphabetic character

       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.

       None.

       The isalpha() and isalpha_l() functions shall return non-zero if c is an alphabetic character; otherwise,
       they shall return 0.

isalnum(),  isblank(),  iscntrl(),  isdigit(),  isgraph(),  islower(),  isprint(),  ispunct(), isspace(),
       isupper(), isxdigit(), setlocale(), uselocale()

       The Base Definitions volume of POSIX.1‐2017, Chapter7, Locale, <ctype.h>, <locale.h>, <stdio.h>

       #include <ctype.h>

       int isalpha(int c);
       int isalpha_l(int c, locale_t locale);