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                                       TOLOWER(3POSIX)

       For tolower(): 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 tolower() and tolower_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  tolower()  or  tolower_l()  represents  an  uppercase  letter,  and  there  exists  a
       corresponding  lowercase  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
       lowercase letter. All other arguments in the domain are returned unchanged.

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

       No errors are defined.

       Thefollowingsectionsareinformative.

       None.

       None.

       tolower, tolower_l — transliterate uppercase characters to lowercase

       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, the tolower() and tolower_l() functions shall  return  the  lowercase  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 tolower(int c);
       int tolower_l(int c, locale_t locale);