Section: POSIX Programmer's Manual (3P)
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.
--- transliterate uppercase characters to lowercase
int tolower(int c);
int tolower_l(int c, locale_t locale);
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.
functions have as a domain a type
the value of which is representable as an
or the value of EOF. If the argument has any other value, the behavior
is undefined. If the argument of
represents an uppercase letter, and there exists a corresponding
lowercase letter as defined by character type information in the current
or in the locale represented by
the result shall be the corresponding lowercase letter. All other
arguments in the domain are returned unchanged.
The behavior is undefined if the
is the special locale object LC_GLOBAL_LOCALE or is not a valid locale
Upon successful completion, the
functions shall return the lowercase letter corresponding to the
argument passed; otherwise, they shall return the argument unchanged.
No errors are defined.
The following sections are informative.
The Base Definitions volume of POSIX.1-2017,
Chapter 7, Locale,
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
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