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
int wctomb(char *s, wchar_t wchar);
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.
function shall determine the number of bytes needed to represent the
character corresponding to the wide-character code whose value is
(including any change in the shift state). It shall store the character
representation (possibly multiple bytes and any special bytes to change
shift state) in the array object pointed to by
is not a null pointer). At most
bytes shall be stored. If
is 0, a null byte shall be stored, preceded by any shift sequence
needed to restore the initial shift state, and
shall be left in the initial shift state.
The behavior of this function is affected by the
category of the current locale. For a state-dependent encoding, this
function shall be placed into its initial state by a call for which its
character pointer argument,
is a null pointer. Subsequent calls with
as other than a null pointer shall cause the internal state of the
function to be altered as necessary. A call with
as a null pointer shall cause this function to return a non-zero value
if encodings have state dependency, and 0 otherwise. Changing the
category causes the shift state of this function to be unspecified.
function need not be thread-safe.
The implementation shall behave as if no function defined in this volume of POSIX.1-2017
is a null pointer,
shall return a non-zero or 0 value, if character encodings,
respectively, do or do not have state-dependent encodings. If
is not a null pointer,
shall return -1 if the value of
does not correspond to a valid character, or return the number of
bytes that constitute the character corresponding to the value of
In no case shall the value returned be greater than the value of the
function shall fail if:
An invalid wide-character code is detected.
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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