libc/stdio/wscanf.3

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.\"     @(#)scanf.3	8.2 (Berkeley) 12/11/93
.\" FreeBSD: src/lib/libc/stdio/scanf.3,v 1.24 2003/06/28 09:03:25 das Exp
.\"
.Dd $Mdocdate: August 30 2019 $
.Dt WSCANF 3
.Os
.Sh NAME
.Nm wscanf ,
.Nm fwscanf ,
.Nm swscanf ,
.Nm vwscanf ,
.Nm vswscanf ,
.Nm vfwscanf
.Nd wide character input format conversion
.Sh SYNOPSIS
.In stdio.h
.In wchar.h
.Ft int
.Fn wscanf "const wchar_t * restrict format" ...
.Ft int
.Fn fwscanf "FILE * restrict stream" "const wchar_t * restrict format" ...
.Ft int
.Fn swscanf "const wchar_t * restrict str" "const wchar_t * restrict format" ...
.In stdarg.h
.Ft int
.Fn vwscanf "const wchar_t * restrict format" "va_list ap"
.Ft int
.Fn vswscanf "const wchar_t * restrict str" "const wchar_t * restrict format" "va_list ap"
.Ft int
.Fn vfwscanf "FILE * restrict stream" "const wchar_t * restrict format" "va_list ap"
.Sh DESCRIPTION
The
.Fn wscanf
family of functions read input according to the given
.Fa format
as described below.
This format may contain
.Dq conversion specifiers ;
the results of such conversions, if any, are stored through a set of pointer
arguments.
.Pp
The
.Fn wscanf
function reads input from the standard input stream
.Em stdin ,
.Fn fwscanf
reads input from the supplied stream pointer
.Fa stream ,
and
.Fn swscanf
reads its input from the wide character string pointed to by
.Fa str .
.Pp
The
.Fn vfwscanf
function is analogous to
.Xr vfwprintf 3
and reads input from the stream pointer
.Fa stream
using a variable argument list of pointers (see
.Xr va_start 3 ) .
The
.Fn vwscanf
function scans a variable argument list from the standard input and the
.Fn vswscanf
function scans it from a wide character string; these are analogous to the
.Fn vwprintf
and
.Fn vswprintf
functions, respectively.
.Pp
Each successive
.Em pointer
argument must correspond properly with each successive conversion specifier
(but see the
.Cm *
conversion below).
All conversions are introduced by the
.Cm %
(percent sign) character.
The
.Fa format
string may also contain other characters.
Whitespace (such as blanks, tabs, or newlines) in the
.Fa format
string match any amount of whitespace, including none, in the input.
Everything else matches only itself.
Scanning stops when an input character does not match such a format character.
Scanning also stops when an input conversion cannot be made (see below).
.Sh CONVERSIONS
Following the
.Cm %
character, introducing a conversion, there may be a number of
.Em flag
characters, as follows:
.Bl -tag -width "ll (ell ell)"
.It Cm *
Suppresses assignment.
The conversion that follows occurs as usual, but no pointer is used;
the result of the conversion is simply discarded.
.It Cm hh
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to a
.Vt char
(rather than
.Vt int ) .
.It Cm h
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to a
.Vt "short int"
(rather than
.Vt int ) .
.It Cm l No (ell)
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to a
.Vt "long int"
(rather than
.Vt int ) ,
that the conversion will be one of
.Cm aefg
and the next pointer is a pointer to
.Vt double
(rather than
.Vt float ) ,
or that the conversion will be one of
.Cm c
or
.Cm s
and the next pointer is a pointer to an array of
.Vt wchar_t
(rather than
.Vt char ) .
.It Cm ll No (ell ell)
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to a
.Vt "long long int"
(rather than
.Vt int ) .
.It Cm L
Indicates that the conversion will be one of
.Cm aefg
and the next pointer is a pointer to
.Vt "long double" .
.It Cm j
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to an
.Vt intmax_t
(rather than
.Vt int ) .
.It Cm t
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to a
.Vt ptrdiff_t
(rather than
.Vt int ) .
.It Cm z
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to a
.Vt size_t
(rather than
.Vt int ) .
.It Cm q
(deprecated)
Indicates that the conversion will be one of
.Cm dioux
or
.Cm n
and the next pointer is a pointer to a
.Vt "long long int"
(rather than
.Vt int ) .
.El
.Pp
In addition to these flags, there may be an optional maximum field width,
expressed as a decimal integer, between the
.Cm %
and the conversion.
If no width is given,
a default of
.Dq infinity
is used (with one exception, below);
otherwise at most this many characters are scanned in processing the
conversion.
Before conversion begins, most conversions skip whitespace;
this whitespace is not counted against the field width.
.Pp
The following conversions are available:
.Bl -tag -width XXXX
.It Cm %
Matches a literal
.Ql % .
That is,
.Dq Li %%
in the format string matches a single input
.Ql %
character.
No conversion is done, and assignment does not occur.
.It Cm d
Matches an optionally signed decimal integer;
the next pointer must be a pointer to
.Vt int .
.It Cm i
Matches an optionally signed integer;
the next pointer must be a pointer to
.Vt int .
The integer is read in base 16 if it begins
with
.Ql 0x
or
.Ql 0X ,
in base 8 if it begins with
.Ql 0 ,
and in base 10 otherwise.
Only characters that correspond to the base are used.
.It Cm o
Matches an octal integer;
the next pointer must be a pointer to
.Vt "unsigned int" .
.It Cm u
Matches an optionally signed decimal integer;
the next pointer must be a pointer to
.Vt "unsigned int" .
.It Cm xX
Matches an optionally signed hexadecimal integer;
the next pointer must be a pointer to
.Vt "unsigned int" .
.It Cm a , A , e , E , f , F , g , G
Matches a floating-point number in the style of
.Xr wcstod 3 .
The next pointer must be a pointer to
.Vt float
(unless
.Cm l
or
.Cm L
is specified.)
.It Cm s
Matches a sequence of non-whitespace wide characters;
the next pointer must be a pointer to
.Vt char ,
and the provided array must be large enough to accept and store
the multibyte representation of the whole sequence and the
terminating NUL character.
The input string stops at whitespace
or at the maximum field width, whichever occurs first.
If specified, the maximum field length refers to the sequence
being scanned rather than the storage space, hence the provided
array must be 1 larger for the terminating NUL character.
.Pp
If an
.Cm l
qualifier is present, the next pointer must be a pointer to
.Vt wchar_t ,
into which the input will be placed.
.It Cm c
Matches a sequence of wide characters consuming the number of wide characters
specified by the field width (defaults to 1 if unspecified);
the next pointer must be a pointer to
.Vt char ,
and there must be enough room for the multibyte representation
of all the characters
(no terminating NUL is added).
The usual skip of leading whitespace is suppressed.
To skip whitespace first, use an explicit space in the format.
.Pp
If an
.Cm l
qualifier is present, the next pointer must be a pointer to
.Vt wchar_t ,
into which the input will be placed.
.It Cm \&[
Matches a nonempty sequence of characters from the specified set
of accepted characters;
the next pointer must be a pointer to
.Vt char ,
and there must be enough room for the multibyte representation of
all the characters in the string,
plus a terminating NUL character.
The usual skip of leading whitespace is suppressed.
.Pp
The string is to be made up of characters in
(or not in)
a particular set;
the set is defined by the characters between the open bracket
.Cm \&[
character
and a close bracket
.Cm \&]
character.
The set
.Em excludes
those characters
if the first character after the open bracket is a circumflex
.Cm ^ .
To include a close bracket in the set,
make it the first character after the open bracket
or the circumflex;
any other position will end the set.
To include a hyphen in the set,
make it the last character before the final close bracket;
some implementations of
.Fn wscanf
use
.Dq Li A-Z
to represent the range of characters between
.Ql A
and
.Ql Z .
The string ends with the appearance of a character not in
(or, with a circumflex, in) the set
or when the field width runs out.
.Pp
If an
.Cm l
qualifier is present, the next pointer must be a pointer to
.Vt wchar_t ,
into which the input will be placed.
.It Cm p
Matches a pointer value (as printed by
.Ql %p
in
.Xr wprintf 3 ) ;
the next pointer must be a pointer to
.Vt void .
.It Cm n
Nothing is expected;
instead, the number of characters consumed thus far from the input
is stored through the next pointer,
which must be a pointer to
.Vt int .
This is
.Em not
a conversion, although it can be suppressed with the
.Cm *
flag.
.El
.Pp
For backwards compatibility, a
.Dq conversion
of
.Ql %\e0
causes an immediate return of
.Dv EOF .
.Sh RETURN VALUES
These functions return the number of input items assigned, which can be fewer
than provided for, or even zero, in the event of a matching failure.
Zero indicates that, while there was input available, no conversions were
assigned; typically this is due to an invalid input character,
such as an alphabetic character for a
.Ql %d
conversion.
The value
.Dv EOF
is returned if an input failure occurs before any conversion such as an
end-of-file occurs.
If an error or end-of-file occurs after conversion has begun,
the number of conversions which were successfully completed is returned.
.Sh SEE ALSO
.Xr fgetwc 3 ,
.Xr scanf 3 ,
.Xr wcrtomb 3 ,
.Xr wcstod 3 ,
.Xr wcstol 3 ,
.Xr wcstoul 3 ,
.Xr wprintf 3
.Sh STANDARDS
The functions
.Fn wscanf ,
.Fn fwscanf ,
.Fn swscanf ,
.Fn vwscanf ,
.Fn vfwscanf ,
and
.Fn vswscanf
conform to
.St -isoC-99 .
.Sh CAVEATS
On systems other than
.Ox ,
the
.Dv LC_NUMERIC
.Xr locale 1
category can cause parsing failures; see CAVEATS in
.Xr setlocale 3
for details.
.Sh BUGS
In addition to the bugs documented in
.Xr scanf 3 ,
.Fn wscanf
does not support the
.Dq Li A-Z
notation for specifying character ranges with the character
class conversion
.Pq Sq Cm %[ .