man3/wprintf.3

.\" Copyright (c) Bruno Haible <haible@clisp.cons.org>
.\"
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.\" References consulted:
.\"   GNU glibc-2 source code and manual
.\"   Dinkumware C library reference http://www.dinkumware.com/
.\"   OpenGroup's Single UNIX specification http://www.UNIX-systems.org/online.html
.\"   ISO/IEC 9899:1999
.\"
.TH WPRINTF 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
wprintf, fwprintf, swprintf, vwprintf, vfwprintf, vswprintf \- formatted
wide-character output conversion
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.B #include <wchar.h>
.PP
.BI "int wprintf(const wchar_t *restrict " format ", ...);"
.BI "int fwprintf(FILE *restrict " stream ,
.BI "             const wchar_t *restrict " format ", ...);"
.BI "int swprintf(wchar_t *restrict " wcs ", size_t " maxlen ,
.BI "             const wchar_t *restrict " format ", ...);"
.PP
.BI "int vwprintf(const wchar_t *restrict " format ", va_list " args );
.BI "int vfwprintf(FILE *restrict " stream ,
.BI "             const wchar_t *restrict " format ", va_list " args );
.BI "int vswprintf(wchar_t *restrict " wcs ", size_t " maxlen ,
.BI "             const wchar_t *restrict " format ", va_list " args );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
All functions shown above:
.\" .BR wprintf (),
.\" .BR fwprintf (),
.\" .BR swprintf (),
.\" .BR vwprintf (),
.\" .BR vfwprintf (),
.\" .BR vswprintf ():
.nf
    _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE
        || _POSIX_C_SOURCE >= 200112L
.fi
.SH DESCRIPTION
The
.BR wprintf ()
family of functions is
the wide-character equivalent of the
.BR printf (3)
family of functions.
It performs formatted output of wide
characters.
.PP
The
.BR wprintf ()
and
.BR vwprintf ()
functions
perform wide-character output to
.IR stdout .
.I stdout
must not be byte oriented; see
.BR fwide (3)
for more information.
.PP
The
.BR fwprintf ()
and
.BR vfwprintf ()
functions
perform wide-character output to
.IR stream .
.I stream
must not be byte oriented; see
.BR fwide (3)
for more information.
.PP
The
.BR swprintf ()
and
.BR vswprintf ()
functions
perform wide-character output
to an array of wide characters.
The programmer must ensure that there is
room for at least
.I maxlen
wide
characters at
.IR wcs .
.PP
These functions are like
the
.BR printf (3),
.BR vprintf (3),
.BR fprintf (3),
.BR vfprintf (3),
.BR sprintf (3),
.BR vsprintf (3)
functions except for the
following differences:
.TP
.B \(bu
The
.I format
string is a wide-character string.
.TP
.B \(bu
The output consists of wide characters, not bytes.
.TP
.B \(bu
.BR swprintf ()
and
.BR vswprintf ()
take a
.I maxlen
argument,
.BR sprintf (3)
and
.BR vsprintf (3)
do not.
.RB ( snprintf (3)
and
.BR vsnprintf (3)
take a
.I maxlen
argument, but these functions do not return \-1 upon
buffer overflow on Linux.)
.PP
The treatment of the conversion characters
.BR c
and
.B s
is different:
.TP
.B c
If no
.B l
modifier is present, the
.I int
argument is converted to a wide character by a call to the
.BR btowc (3)
function, and the resulting wide character is written.
If an
.B l
modifier is present, the
.I wint_t
(wide character) argument is written.
.TP
.B s
If no
.B l
modifier is present: the
.I "const\ char\ *"
argument is expected to be a pointer to an array of character type
(pointer to a string) containing a multibyte character sequence beginning
in the initial shift state.
Characters from the array are converted to
wide characters (each by a call to the
.BR mbrtowc (3)
function with a conversion state starting in the initial state before
the first byte).
The resulting wide characters are written up to
(but not including) the terminating null wide character (L\(aq\e0\(aq).
If a precision is
specified, no more wide characters than the number specified are written.
Note that the precision determines the number of
.I wide characters
written, not the number of
.I bytes
or
.IR "screen positions" .
The array must contain a terminating null byte (\(aq\e0\(aq),
unless a precision is given
and it is so small that the number of converted wide characters reaches it
before the end of the array is reached.
If an
.B l
modifier is present: the
.I "const\ wchar_t\ *"
argument is expected to be a pointer to an array of wide characters.
Wide characters from the array are written up to (but not including) a
terminating null wide character.
If a precision is specified, no more than
the number specified are written.
The array must contain a terminating null
wide character, unless a precision is given and it is smaller than or equal
to the number of wide characters in the array.
.SH RETURN VALUE
The functions return the number of wide characters written, excluding the
terminating null wide character in
case of the functions
.BR swprintf ()
and
.BR vswprintf ().
They return \-1 when an error occurs.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR wprintf (),
.BR fwprintf (),
.BR swprintf (),
.BR vwprintf (),
.BR vfwprintf (),
.BR vswprintf ()
T}	Thread safety	MT-Safe locale
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99.
.SH NOTES
The behavior of
.BR wprintf ()
et al. depends
on the
.B LC_CTYPE
category of the
current locale.
.PP
If the
.I format
string contains non-ASCII wide characters, the program
will work correctly only if the
.B LC_CTYPE
category of the current locale at
run time is the same as the
.B LC_CTYPE
category of the current locale at
compile time.
This is because the
.I wchar_t
representation is platform- and locale-dependent.
(The glibc represents
wide characters using their Unicode (ISO-10646) code point, but other
platforms don't do this.
Also, the use of C99 universal character names
of the form \eunnnn does not solve this problem.)
Therefore, in
internationalized programs, the
.I format
string should consist of ASCII
wide characters only, or should be constructed at run time in an
internationalized way (e.g., using
.BR gettext (3)
or
.BR iconv (3),
followed by
.BR mbstowcs (3)).
.SH SEE ALSO
.BR fprintf (3),
.BR fputwc (3),
.BR fwide (3),
.BR printf (3),
.BR snprintf (3)
.\" .BR wscanf (3)