.\" $NetBSD: mbsrtowcs.3,v 1.15 2024/09/09 18:55:26 wiz Exp $
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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
.
.In 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:
.Bl -bullet
.It
The conversion reaches a NUL byte.
In this case, the NUL byte is also converted.
.It
The
.Fn mbsrtowcs
has already stored
.Fa n
wide characters.
.It
The conversion encounters an invalid character.
.El
.Pp
Each character will be converted as if
.Xr mbrtowc 3
is continuously called.
.Pp
After conversion,
if
.Fa pwcs
is not a NULL pointer,
the pointer object pointed to by
.Fa s
is a NULL pointer
.Pq if the conversion is stopped due to reaching a NUL byte
or the first byte of the character just after the last character
converted.
.Pp
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.
.Pp
The behaviour of
.Fn mbsrtowcs
is affected by the
.Dv LC_CTYPE
category of the current locale.
.Pp
These are the special cases:
.Bl -tag -width Li
.
.It Li "s == NULL || *s == NULL"
Undefined (may cause the program to crash).
.
.It 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.
.
.It 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.
.Pp
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
.Pp
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:
.Bl -tag -width Li
.It 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.
.It 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:
.Bl -tag -width Er
.It Bq Er EILSEQ
.Fa s
points to a string containing an invalid or incomplete multibyte
character.
.It 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 .
.Pp
The
.Fn mbsnrtowcs
function conforms to
.St -p1003.1-2008 .