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'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.TH wcstombs 3 2025-06-28 "Linux man-pages (unreleased)"
.SH NAME
wcstombs \- convert a wide-character string to a multibyte string
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.P
.BR "size_t wcstombs(" "size_t n;"
.BI " char " dest "[restrict " n "], \
const wchar_t *restrict " src ,
.BI " size_t " n );
.fi
.SH DESCRIPTION
If
.I dest
is not NULL, the
.BR wcstombs ()
function converts
the wide-character string
.I src
to a multibyte string starting at
.IR dest .
At most
.I n
bytes are written to
.IR dest .
The sequence of characters placed in
.I dest
begins in the initial shift state.
The conversion can stop for three reasons:
.IP \[bu] 3
A wide character has been encountered that can not be represented as a
multibyte sequence (according to the current locale).
In this case,
.I (size_t)\ \-1
is returned.
.IP \[bu]
The length limit forces a stop.
In this case, the number of bytes written to
.I dest
is returned, but the shift state at this point is lost.
.IP \[bu]
The wide-character string has been completely converted, including the
terminating null wide character (L\[aq]\[rs]0\[aq]).
In this case, the conversion ends in the initial shift state.
The number of bytes written to
.IR dest ,
excluding the terminating null byte (\[aq]\[rs]0\[aq]), is returned.
.P
The programmer must ensure that there is room for at least
.I n
bytes
at
.IR dest .
.P
If
.I dest
is NULL,
.I n
is ignored, and the conversion proceeds as
above, except that the converted bytes are not written out to memory,
and no length limit exists.
.P
In order to avoid the case 2 above, the programmer should make sure
.I n
is greater than or equal to
.IR "wcstombs(NULL,src,0)+1" .
.SH RETURN VALUE
The
.BR wcstombs ()
function returns the number of bytes that make up the
converted part of a multibyte sequence,
not including the terminating null byte.
If a wide character was encountered which could not be
converted,
.I (size_t)\ \-1
is returned.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR wcstombs ()
T} Thread safety MT-Safe
.TE
.SH VERSIONS
The function
.BR wcsrtombs (3)
provides a better interface to the same functionality.
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
POSIX.1-2001, C99.
.SH NOTES
The behavior of
.BR wcstombs ()
depends on the
.B LC_CTYPE
category of the
current locale.
.SH SEE ALSO
.BR mblen (3),
.BR mbstowcs (3),
.BR mbtowc (3),
.BR wcsrtombs (3),
.BR wctomb (3)
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