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

       None.

       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                                       TOUPPER(3POSIX)

       For toupper(): 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 toupper() and toupper_l() functions have as a domain a type int, the value of which is  representable
       as an unsignedchar or the value of EOF. If the argument has any other value, the behavior is undefined.

       If  the  argument  of  toupper()  or  toupper_l()  represents  a  lowercase  letter,  and  there exists a
       corresponding uppercase letter as defined by character type information in the current locale or  in  the
       locale  represented  by  locale,  respectively (category LC_CTYPE), the result shall be the corresponding
       uppercase letter.

       All other arguments in the domain are returned unchanged.

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

       No errors are defined.

       Thefollowingsectionsareinformative.

       None.

       None.

       toupper, toupper_l — transliterate lowercase characters to uppercase

       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.

       Upon  successful completion, toupper() and toupper_l() shall return the uppercase letter corresponding to
       the argument passed; otherwise, they shall return the argument unchanged.

setlocale(), uselocale()

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

       #include <ctype.h>

       int toupper(int c);
       int toupper_l(int c, locale_t locale);