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       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       fwscanf, swscanf, wscanf — convert formatted wide-character input

SYNOPSIS

       #include <stdio.h>
       #include <wchar.h>

       int fwscanf(FILE *restrict stream, const wchar_t *restrict format, ...);
       int swscanf(const wchar_t *restrict ws,
           const wchar_t *restrict format, ...);
       int wscanf(const wchar_t *restrict format, ...);

DESCRIPTION

The functionality described on this reference page is aligned with the ISO C standard. Any
conflict between the requirements described here and the ISO C standard is unintentional.
This volume of POSIX.1‐2017 defers to the ISO C standard.

The fwscanf() function shall read from the named input stream. The wscanf() function
shall read from the standard input stream stdin. The swscanf() function shall read from
the wide-character string ws. Each function reads wide characters, interprets them
according to a format, and stores the results in its arguments. Each expects, as
arguments, a control wide-character string format described below, and a set of pointer
arguments indicating where the converted input should be stored. The result is undefined
if there are insufficient arguments for the format. If the format is exhausted while
arguments remain, the excess arguments are evaluated but are otherwise ignored.

Conversions can be applied to the nth argument after the format in the argument list,
rather than to the next unused argument. In this case, the conversion specifier wide
character % (see below) is replaced by the sequence "%n$", where n is a decimal integer in
the range [1,{NL_ARGMAX}]. This feature provides for the definition of format wide-
character strings that select arguments in an order appropriate to specific languages. In
format wide-character strings containing the "%n$" form of conversion specifications, it
is unspecified whether numbered arguments in the argument list can be referenced from the
format wide-character string more than once.

The format can contain either form of a conversion specification—that is, % or "%n$"— but
the two forms cannot normally be mixed within a single format wide-character string. The
only exception to this is that %% or %* can be mixed with the "%n$" form. When numbered
argument specifications are used, specifying the Nth argument requires that all the
leading arguments, from the first to the (N-1)th, are pointers.

The fwscanf() function in all its forms allows for detection of a language-dependent radix
character in the input string, encoded as a wide-character value. The radix character is
defined in the current locale (category LC_NUMERIC). In the POSIX locale, or in a locale
where the radix character is not defined, the radix character shall default to a <period>
('.').

The format is a wide-character string composed of zero or more directives. Each directive
is composed of one of the following: one or more white-space wide characters (<space>,
<tab>, <newline>, <vertical-tab>, or <form-feed>); an ordinary wide character (neither '%'
nor a white-space character); or a conversion specification. It is unspecified whether an
encoding error occurs if the format string contains wchar_t values that do not correspond
to members of the character set of the current locale and the specified semantics do not
require that value to be processed by wcrtomb().

Each conversion specification is introduced by the '%' or by the character sequence "%n$",
after which the following appear in sequence:

* An optional assignment-suppressing character '*'.

* An optional non-zero decimal integer that specifies the maximum field width.

* An optional assignment-allocation character 'm'.

* An optional length modifier that specifies the size of the receiving object.

* A conversion specifier wide character that specifies the type of conversion to be
applied. The valid conversion specifiers are described below.

The fwscanf() functions shall execute each directive of the format in turn. If a directive
fails, as detailed below, the function shall return. Failures are described as input
failures (due to the unavailability of input bytes) or matching failures (due to
inappropriate input).

A directive composed of one or more white-space wide characters is executed by reading
input until no more valid input can be read, or up to the first wide character which is
not a white-space wide character, which remains unread.

A directive that is an ordinary wide character shall be executed as follows. The next wide
character is read from the input and compared with the wide character that comprises the
directive; if the comparison shows that they are not equivalent, the directive shall fail,
and the differing and subsequent wide characters remain unread. Similarly, if end-of-file,
an encoding error, or a read error prevents a wide character from being read, the
directive shall fail.

A directive that is a conversion specification defines a set of matching input sequences,
as described below for each conversion wide character. A conversion specification is
executed in the following steps.

Input white-space wide characters (as specified by iswspace()) shall be skipped, unless
the conversion specification includes a [, c, or n conversion specifier.

An item shall be read from the input, unless the conversion specification includes an n
conversion specifier wide character. An input item is defined as the longest sequence of
input wide characters, not exceeding any specified field width, which is an initial
subsequence of a matching sequence. The first wide character, if any, after the input
item shall remain unread. If the length of the input item is zero, the execution of the
conversion specification shall fail; this condition is a matching failure, unless end-of-
file, an encoding error, or a read error prevented input from the stream, in which case it
is an input failure.

Except in the case of a % conversion specifier, the input item (or, in the case of a %n
conversion specification, the count of input wide characters) shall be converted to a type
appropriate to the conversion wide character. If the input item is not a matching
sequence, the execution of the conversion specification shall fail; this condition is a
matching failure. Unless assignment suppression was indicated by a '*', the result of the
conversion shall be placed in the object pointed to by the first argument following the
format argument that has not already received a conversion result if the conversion
specification is introduced by %, or in the nth argument if introduced by the wide-
character sequence "%n$". If this object does not have an appropriate type, or if the
result of the conversion cannot be represented in the space provided, the behavior is
undefined.

The %c, %s, and %[ conversion specifiers shall accept an optional assignment-allocation
character 'm', which shall cause a memory buffer to be allocated to hold the wide-
character string converted including a terminating null wide character. In such a case,
the argument corresponding to the conversion specifier should be a reference to a pointer
value that will receive a pointer to the allocated buffer. The system shall allocate a
buffer as if malloc() had been called. The application shall be responsible for freeing
the memory after usage. If there is insufficient memory to allocate a buffer, the function
shall set errno to [ENOMEM] and a conversion error shall result. If the function returns
EOF, any memory successfully allocated for parameters using assignment-allocation
character 'm' by this call shall be freed before the function returns.

The length modifiers and their meanings are:

hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to
an argument with type pointer to signed char or unsigned char.

h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to
an argument with type pointer to short or unsigned short.

l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to
an argument with type pointer to long or unsigned long; that a following a, A, e,
E, f, F, g, or G conversion specifier applies to an argument with type pointer to
double; or that a following c, s, or [ conversion specifier applies to an argument
with type pointer to wchar_t. If the 'm' assignment-allocation character is
specified, the conversion applies to an argument with the type pointer to a
pointer to wchar_t.

ll (ell-ell)
Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to
an argument with type pointer to long long or unsigned long long.

j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to
an argument with type pointer to intmax_t or uintmax_t.

z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to
an argument with type pointer to size_t or the corresponding signed integer type.

t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to
an argument with type pointer to ptrdiff_t or the corresponding unsigned type.

L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies
to an argument with type pointer to long double.

If a length modifier appears with any conversion specifier other than as specified above,
the behavior is undefined.

The following conversion specifier wide characters are valid:

d Matches an optionally signed decimal integer, whose format is the same as expected
for the subject sequence of wcstol() with the value 10 for the base argument. In
the absence of a size modifier, the application shall ensure that the
corresponding argument is a pointer to int.

i Matches an optionally signed integer, whose format is the same as expected for the
subject sequence of wcstol() with 0 for the base argument. In the absence of a
size modifier, the application shall ensure that the corresponding argument is a
pointer to int.

o Matches an optionally signed octal integer, whose format is the same as expected
for the subject sequence of wcstoul() with the value 8 for the base argument. In
the absence of a size modifier, the application shall ensure that the
corresponding argument is a pointer to unsigned.

u Matches an optionally signed decimal integer, whose format is the same as expected
for the subject sequence of wcstoul() with the value 10 for the base argument. In
the absence of a size modifier, the application shall ensure that the
corresponding argument is a pointer to unsigned.

x Matches an optionally signed hexadecimal integer, whose format is the same as
expected for the subject sequence of wcstoul() with the value 16 for the base
argument. In the absence of a size modifier, the application shall ensure that the
corresponding argument is a pointer to unsigned.

a, e, f, g
Matches an optionally signed floating-point number, infinity, or NaN whose format
is the same as expected for the subject sequence of wcstod(). In the absence of a
size modifier, the application shall ensure that the corresponding argument is a
pointer to float.

If the fwprintf() family of functions generates character string representations
for infinity and NaN (a symbolic entity encoded in floating-point format) to
support IEEE Std 754‐1985, the fwscanf() family of functions shall recognize them
as input.

s Matches a sequence of non-white-space wide characters. If no l (ell) qualifier is
present, characters from the input field shall be converted as if by repeated
calls to the wcrtomb() function, with the conversion state described by an
mbstate_t object initialized to zero before the first wide character is converted.
If the 'm' assignment-allocation character is not specified, the application shall
ensure that the corresponding argument is a pointer to a character array large
enough to accept the sequence and the terminating null character, which shall be
added automatically. Otherwise, the application shall ensure that the
corresponding argument is a pointer to a pointer to a wchar_t.

If the l (ell) qualifier is present and the 'm' assignment-allocation character is
not specified, the application shall ensure that the corresponding argument is a
pointer to an array of wchar_t large enough to accept the sequence and the
terminating null wide character, which shall be added automatically. If the l
(ell) qualifier is present and the 'm' assignment-allocation character is present,
the application shall ensure that the corresponding argument is a pointer to a
pointer to a wchar_t.

[ Matches a non-empty sequence of wide characters from a set of expected wide
characters (the scanset). If no l (ell) qualifier is present, wide characters
from the input field shall be converted as if by repeated calls to the wcrtomb()
function, with the conversion state described by an mbstate_t object initialized
to zero before the first wide character is converted. If the 'm' assignment-
allocation character is not specified, the application shall ensure that the
corresponding argument is a pointer to a character array large enough to accept
the sequence and the terminating null character, which shall be added
automatically. Otherwise, the application shall ensure that the corresponding
argument is a pointer to a pointer to a wchar_t.

If an l (ell) qualifier is present and the 'm' assignment-allocation character is
not specified, the application shall ensure that the corresponding argument is a
pointer to an array of wchar_t large enough to accept the sequence and the
terminating null wide character. If an l (ell) qualifier is present and the 'm'
assignment-allocation character is specified, the application shall ensure that
the corresponding argument is a pointer to a pointer to a wchar_t.

The conversion specification includes all subsequent wide characters in the format
string up to and including the matching <right-square-bracket> (']'). The wide
characters between the square brackets (the scanlist) comprise the scanset, unless
the wide character after the <left-square-bracket> is a <circumflex> ('^'), in
which case the scanset contains all wide characters that do not appear in the
scanlist between the <circumflex> and the <right-square-bracket>. If the
conversion specification begins with "[]" or "[^]", the <right-square-bracket> is
included in the scanlist and the next <right-square-bracket> is the matching
<right-square-bracket> that ends the conversion specification; otherwise, the
first <right-square-bracket> is the one that ends the conversion specification. If
a '-' is in the scanlist and is not the first wide character, nor the second where
the first wide character is a '^', nor the last wide character, the behavior is
implementation-defined.

c Matches a sequence of wide characters of exactly the number specified by the field
width (1 if no field width is present in the conversion specification).

If no l (ell) length modifier is present, characters from the input field shall be
converted as if by repeated calls to the wcrtomb() function, with the conversion
state described by an mbstate_t object initialized to zero before the first wide
character is converted. No null character is added. If the 'm' assignment-
allocation character is not specified, the application shall ensure that the
corresponding argument is a pointer to the initial element of a character array
large enough to accept the sequence. Otherwise, the application shall ensure that
the corresponding argument is a pointer to a pointer to a char.

No null wide character is added. If an l (ell) length modifier is present and the
'm' assignment-allocation character is not specified, the application shall ensure
that the corresponding argument shall be a pointer to the initial element of an
array of wchar_t large enough to accept the sequence. If an l (ell) qualifier is
present and the 'm' assignment-allocation character is specified, the application
shall ensure that the corresponding argument is a pointer to a pointer to a
wchar_t.

p Matches an implementation-defined set of sequences, which shall be the same as the
set of sequences that is produced by the %p conversion specification of the
corresponding fwprintf() functions. The application shall ensure that the
corresponding argument is a pointer to a pointer to void. The interpretation of
the input item is implementation-defined. If the input item is a value converted
earlier during the same program execution, the pointer that results shall compare
equal to that value; otherwise, the behavior of the %p conversion is undefined.

n No input is consumed. The application shall ensure that the corresponding argument
is a pointer to the integer into which is to be written the number of wide
characters read from the input so far by this call to the fwscanf() functions.
Execution of a %n conversion specification shall not increment the assignment
count returned at the completion of execution of the function. No argument shall
be converted, but one shall be consumed. If the conversion specification includes
an assignment-suppressing wide character or a field width, the behavior is
undefined.

C Equivalent to lc.

S Equivalent to ls.

% Matches a single '%' wide character; no conversion or assignment shall occur. The
complete conversion specification shall be %%.

If a conversion specification is invalid, the behavior is undefined.

The conversion specifiers A, E, F, G, and X are also valid and shall be equivalent to,
respectively, a, e, f, g, and x.

If end-of-file is encountered during input, conversion is terminated. If end-of-file
occurs before any wide characters matching the current conversion specification (except
for %n) have been read (other than leading white-space, where permitted), execution of the
current conversion specification shall terminate with an input failure. Otherwise, unless
execution of the current conversion specification is terminated with a matching failure,
execution of the following conversion specification (if any) shall be terminated with an
input failure.

Reaching the end of the string in swscanf() shall be equivalent to encountering end-of-
file for fwscanf().

If conversion terminates on a conflicting input, the offending input shall be left unread
in the input. Any trailing white space (including <newline>) shall be left unread unless
matched by a conversion specification. The success of literal matches and suppressed
assignments is only directly determinable via the %n conversion specification.

The fwscanf() and wscanf() functions may mark the last data access timestamp of the file
associated with stream for update. The last data access timestamp shall be marked for
update by the first successful execution of fgetwc(), fgetws(), fwscanf(), getwc(),
getwchar(), vfwscanf(), vwscanf(), or wscanf() using stream that returns data not supplied
by a prior call to ungetwc().

RETURN VALUE

       Upon successful completion, these  functions  shall  return  the  number  of  successfully
       matched  and  assigned  input  items;  this  number  can  be zero in the event of an early
       matching failure. If the input ends before the first conversion (if  any)  has  completed,
       and  without a matching failure having occurred, EOF shall be returned. If an error occurs
       before the first conversion (if any) has completed, and without a matching failure  having
       occurred,  EOF  shall be returned and errno shall be set to indicate the error.  If a read
       error occurs, the error indicator for the stream shall be set.

ERRORS

       For the conditions under which the fwscanf() functions shall fail and may fail,  refer  to
       fgetwc().

       In addition, the fwscanf() function shall fail if:

       EILSEQ Input byte sequence does not form a valid character.

       ENOMEM Insufficient storage space is available.

       In addition, the fwscanf() function may fail if:

       EINVAL There are insufficient arguments.

       The following sections are informative.

EXAMPLES

       The call:

           int i, n; float x; char name[50];
           n = wscanf(L"%d%f%s", &i, &x, name);

       with the input line:

           25 54.32E-1 Hamster

       assigns  to  n the value 3, to i the value 25, to x the value 5.432, and name contains the
       string "Hamster".

       The call:

           int i; float x; char name[50];
           (void) wscanf(L"%2d%f%*d %[0123456789]", &i, &x, name);

       with input:

           56789 0123 56a72

       assigns 56 to i, 789.0 to x, skips 0123, and places the string "56\0" in name.   The  next
       call to getchar() shall return the character 'a'.

APPLICATION USAGE

       In  format  strings containing the '%' form of conversion specifications, each argument in
       the argument list is used exactly once.

       For functions that allocate memory as if by malloc(), the application should release  such
       memory  when  it is no longer required by a call to free().  For fwscanf(), this is memory
       allocated via use of the 'm' assignment-allocation character.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  by
       the  Institute  of  Electrical  and Electronics Engineers, Inc and The Open Group.  In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .