.\" Copyright (c) 2002-2004 Tim J. Robbins
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.Dd May 21, 2013
.Dt MBRTOWC 3
.Os
.Sh NAME
.Nm mbrtowc ,
.Nm mbrtoc16 ,
.Nm mbrtoc32
.Nd "convert a character to a wide-character code (restartable)"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In wchar.h
.Ft size_t
.Fo mbrtowc
.Fa "wchar_t * restrict pc" "const char * restrict s" "size_t n"
.Fa "mbstate_t * restrict ps"
.Fc
.In uchar.h
.Ft size_t
.Fo mbrtoc16
.Fa "char16_t * restrict pc" "const char * restrict s" "size_t n"
.Fa "mbstate_t * restrict ps"
.Fc
.Ft size_t
.Fo mbrtoc32
.Fa "char32_t * restrict pc" "const char * restrict s" "size_t n"
.Fa "mbstate_t * restrict ps"
.Fc
.Sh DESCRIPTION
The
.Fn mbrtowc ,
.Fn mbrtoc16
and
.Fn mbrtoc32
functions inspect at most
.Fa n
bytes pointed to by
.Fa s
to determine the number of bytes needed to complete the next multibyte
character.
If a character can be completed, and
.Fa pc
is not
.Dv NULL ,
the wide character which is represented by
.Fa s
is stored in the
.Vt wchar_t ,
.Vt char16_t
or
.Vt char32_t
it points to.
.Pp
If
.Fa s
is
.Dv NULL ,
these functions behave as if
.Fa pc
was
.Dv NULL ,
.Fa s
was an empty string
.Pq Qq
and
.Fa n
was 1.
.Pp
The
.Vt mbstate_t
argument,
.Fa ps ,
is used to keep track of the shift state.
If it is
.Dv NULL ,
these functions use an internal, static
.Vt mbstate_t
object, which is initialized to the initial conversion state
at program startup.
.Pp
As a single
.Vt char16_t
is not large enough to represent certain multibyte characters, the
.Fn mbrtoc16
function may need to be invoked multiple times to convert a single
multibyte character sequence.
.Sh RETURN VALUES
The
.Fn mbrtowc ,
.Fn mbrtoc16
and
.Fn mbrtoc32
functions return:
.Bl -tag -width indent
.It 0
The next
.Fa n
or fewer bytes
represent the null wide character
.Pq Li "L'\e0'" .
.It >0
The next
.Fa n
or fewer bytes represent a valid character, these functions
return the number of bytes used to complete the multibyte character.
.It Po Vt size_t Pc Ns \-1
An encoding error has occurred.
The next
.Fa n
or fewer bytes do not contribute to a valid multibyte character.
.It Po Vt size_t Pc Ns \-2
The next
.Fa n
contribute to, but do not complete, a valid multibyte character sequence,
and all
.Fa n
bytes have been processed.
.El
.Pp
The
.Fn mbrtoc16
function also returns:
.Bl -tag -width indent
.It Po Vt size_t Pc Ns \-3
The next character resulting from a previous call has been stored.
No bytes from the input have been consumed.
.El
.Sh ERRORS
The
.Fn mbrtowc ,
.Fn mbrtoc16
and
.Fn mbrtoc32
functions will fail if:
.Bl -tag -width Er
.It Bq Er EILSEQ
An invalid multibyte sequence was detected.
.It Bq Er EINVAL
The conversion state is invalid.
.El
.Sh SEE ALSO
.Xr mbtowc 3 ,
.Xr multibyte 3 ,
.Xr setlocale 3 ,
.Xr wcrtomb 3
.Sh STANDARDS
The
.Fn mbrtowc ,
.Fn mbrtoc16
and
.Fn mbrtoc32
functions conform to
.St -isoC-2011 .