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 $NetBSD: mbsrtowcs.3,v 1.15 2024/09/09 18:55:26 wiz Exp $

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 All rights reserved.

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.Dd September 9, 2024
.Dt MBSRTOWCS 3
.Os
 ----------------------------------------------------------------------
.Sh NAME
.Nm mbsrtowcs ,
.Nm mbsrntowcs
.Nd converts a multibyte character string to a wide-character string \
(restartable)
 ----------------------------------------------------------------------
.Sh LIBRARY
.Lb libc
 ----------------------------------------------------------------------
.Sh SYNOPSIS
.
n wchar.h .
.Ft size_t
.Fo mbsrtowcs
.Fa "wchar_t * restrict pwcs"
.Fa "const char ** restrict s"
.Fa "size_t n"
.Fa "mbstate_t * restrict ps"
.Fc
.
.Ft size_t
.Fo mbsnrtowcs
.Fa "wchar_t * restrict pwcs"
.Fa "const char ** restrict s"
.Fa "size_t nmc"
.Fa "size_t n"
.Fa "mbstate_t * restrict ps"
.Fc
.
 ----------------------------------------------------------------------
.Sh DESCRIPTION
The
.Fn mbsrtowcs
function converts the multibyte character string indirectly pointed to
by
.Fa s
to the corresponding wide-character string, and stores it in the
array pointed to by
.Fa pwcs .
The conversion stops due to the following reasons:
l -bullet t The conversion reaches a NUL byte.
In this case, the NUL byte is also converted.
t The
.Fn mbsrtowcs
has already stored
.Fa n
wide characters.
t The conversion encounters an invalid character.
.El

p
Each character will be converted as if
.Xr mbrtowc 3
is continuously called.

p
After conversion,
if
.Fa pwcs
is not a NULL pointer,
the pointer object pointed to by
.Fa s
is a NULL pointer

q if the conversion is stopped due to reaching a NUL byte
or the first byte of the character just after the last character
converted.

p
If
.Fa pwcs
is not a NULL pointer and the conversion is stopped due to reaching
a NUL byte, the
.Fn mbsrtowcs
places the state object pointed to by
.Fa ps
to an initial state after the conversion has taken place.

p
The behaviour of
.Fn mbsrtowcs
is affected by the
.Dv LC_CTYPE
category of the current locale.

p
These are the special cases:
l -tag -width Li .
t Li "s == NULL || *s == NULL" Undefined (may cause the program to crash).
.
t Li "pwcs == NULL" The conversion has taken place, but the resulting wide-character string
was discarded.
In this case, the pointer object pointed to by
.Fa s
is not modified and
.Fa n
is ignored.
.
t Li "ps == NULL" The
.Fn mbsrtowcs
uses its own internal state object to keep the conversion state,
instead of
.Fa ps
mentioned in this manual page.

p
Calling any other functions in
.Lb libc
never changes the internal state of
.Fn mbsrtowcs ,
which is initialized at startup time of the program.
.El

p
The
.Fn mbsnrtowcs
function behaves identically to
.Fn mbsrtowcs ,
except that the conversion stops after reading at most
.Fa nmc
characters from the buffer pointed to by
.Fa s .
 ----------------------------------------------------------------------
.Sh RETURN VALUES
The
.Fn mbsrtowcs
and
.Fn mbsnrtowcs
functions return:
l -tag -width Li t Li 0 , No or positive The value returned is the number of elements stored in the array
pointed to by
.Fa pwcs ,
except for a terminating NUL wide character (if any).
If
.Fa pwcs
is not
.Dv NULL
and the value returned is equal to
.Fa n ,
the wide-character string pointed to by
.Fa pwcs
is not NUL-terminated.
If
.Fa pwcs
is a NULL pointer, the value returned is the number of elements to contain
the whole string converted, except for a terminating NUL wide character.
t Li "(size_t)-1" The array indirectly pointed to by
.Fa s
contains a byte sequence forming invalid character.
In this case,
.Fn mbsrtowcs
sets
.Va errno
to indicate the error.
.El
 ----------------------------------------------------------------------
.Sh ERRORS
The
.Fn mbsrtowcs
and
.Fn mbsnrtowcs
functions may fail with the following errors:
l -tag -width Er t Bq Er EILSEQ .Fa s
points to a string containing an invalid or incomplete multibyte
character.
t Bq Er EINVAL .Fa ps
points to an invalid or uninitialized mbstate_t object.
.El
 ----------------------------------------------------------------------
.Sh SEE ALSO
.Xr mbrtowc 3 ,
.Xr mbstowcs 3 ,
.Xr setlocale 3
 ----------------------------------------------------------------------
.Sh STANDARDS
The
.Fn mbsrtowcs
function conforms to
.St -isoC-amd1 .
The
.Li restrict
qualifier was added by
.St -isoC-99 .

p
The
.Fn mbsnrtowcs
function conforms to
.St -p1003.1-2008 .