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.
--- convert a wide-character code to a character (restartable)
size_t wcrtomb(char *restrict s, wchar_t wc, mbstate_t *restrict ps);
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.
is a null pointer, the
function shall be equivalent to the call:
wcrtomb(buf, L'\0', ps)
is an internal buffer.
is not a null pointer, the
function shall determine the number of bytes needed to represent the
character that corresponds to the wide character given by
(including any shift sequences), and store the resulting bytes in the
array whose first element is pointed to by
bytes are stored. If
is a null wide character, a null byte shall be stored, preceded by any
shift sequence needed to restore the initial shift state. The resulting
state described shall be the initial conversion state.
is a null pointer, the
function shall use its own internal
object, which is initialized at program start-up to the initial
conversion state. Otherwise, the
object pointed to by
shall be used to completely describe the current conversion state of
the associated character sequence. The implementation shall behave as
if no function defined in this volume of POSIX.1-2017 calls
function need not be thread-safe if called with a NULL
The behavior of this function shall be affected by the
category of the current locale.
function shall not change the setting of
function shall return the number of bytes stored in the array object
(including any shift sequences). When
is not a valid wide character, an encoding error shall occur. In this
case, the function shall store the value of the macro
and shall return (size_t
)-1; the conversion state shall be
function shall fail if:
An invalid wide-character code is detected.
function may fail if:
points to an object that contains an invalid conversion state.
The following sections are informative.
The Base Definitions volume of POSIX.1-2017,
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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