.\" $NetBSD: mbrtowc.3,v 1.8 2006/10/16 09:10:29 wiz Exp $
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.Dd February 4, 2002
.Dt MBRTOWC 3
.Os
.\" ----------------------------------------------------------------------
.Sh NAME
.Nm mbrtowc
.Nd converts a multibyte character to a wide character (restartable)
.\" ----------------------------------------------------------------------
.Sh LIBRARY
.Lb libc
.\" ----------------------------------------------------------------------
.Sh SYNOPSIS
.In wchar.h
.Ft size_t
.Fn mbrtowc "wchar_t * restrict pwc" "const char * restrict s" "size_t n" \
"mbstate_t * restrict ps"
.\" ----------------------------------------------------------------------
.Sh DESCRIPTION
The
.Fn mbrtowc
usually converts the multibyte character pointed to by
.Fa s
to a wide character, and stores the wide character
to the wchar_t object pointed to by
.Fa pwc
if
.Fa pwc
is
.Pf non- Dv NULL
and
.Fa s
points to a valid character.
The conversion happens in accordance with, and changes the conversion
state described in the mbstate_t object pointed to by
.Fa ps .
This function may examine at most
.Fa n
bytes of the array beginning from
.Fa s .
.Pp
If
.Fa s
points to a valid character and the character corresponds to a nul wide
character, then the
.Fn mbrtowc
places the mbstate_t object pointed to by
.Fa ps
to an initial conversion state.
.Pp
Unlike
.Xr mbtowc 3 ,
the
.Fn mbrtowc
may accept the byte sequence pointed to by
.Fa s
not forming a complete multibyte character
but which may be part of a valid character.
In this case, this function will accept all such bytes
and save them into the conversion state object pointed to by
.Fa ps .
They will be used at subsequent calls of this function to restart
the conversion suspended.
.Pp
The behaviour of
.Fn mbrtowc
is affected by the
.Dv LC_CTYPE
category of the current locale.
.Pp
These are the special cases:
.Bl -tag -width 012345678901
.It "s == NULL"
.Fn mbrtowc
sets the conversion state object pointed to by
.Fa ps
to an initial state and always returns 0.
Unlike
.Xr mbtowc 3 ,
the value returned does not indicate whether the current encoding of
the locale is state-dependent.
.Pp
In this case,
.Fn mbrtowc
ignores
.Fa pwc
and
.Fa n ,
and is equivalent to the following call:
.Bd -literal -offset indent
mbrtowc(NULL, "", 1, ps);
.Ed
.It "pwc == NULL"
The conversion from a multibyte character to a wide character has
taken place and the conversion state may be affected, but the resulting
wide character is discarded.
.It "ps == NULL"
.Fn mbrtowc
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 mbrtowc ,
which is initialized at startup time of the program.
.El
.\" ----------------------------------------------------------------------
.Sh RETURN VALUES
In the usual cases,
.Fn mbrtowc
returns:
.Bl -tag -width 012345678901
.It 0
The next bytes pointed to by
.Fa s
form a nul character.
.It positive
If
.Fa s
points to a valid character,
.Fn mbrtowc
returns the number of bytes in the character.
.It (size_t)-2
.Fa s
points to a byte sequence which possibly contains part of a valid
multibyte character, but which is incomplete.
When
.Fa n
is at least
.Dv MB_CUR_MAX ,
this case can only occur if the array pointed to by
.Fa s
contains a redundant shift sequence.
.It (size_t)-1
.Fa s
points to an illegal byte sequence which does not form a valid multibyte
character.
In this case,
.Fn mbrtowc
sets
.Va errno
to indicate the error.
.El
.\" ----------------------------------------------------------------------
.Sh ERRORS
.Fn mbrtowc
may cause an error in the following case:
.Bl -tag -width Er
.It Bq Er EILSEQ
.Fa s
points to 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 mbrlen 3 ,
.Xr mbtowc 3 ,
.Xr setlocale 3
.\" ----------------------------------------------------------------------
.Sh STANDARDS
The
.Fn mbrtowc
function conforms to
.St -isoC-amd1 .
The restrict qualifier is added at
.St -isoC-99 .