# fwscanf

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of 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 _n_ th 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 _N_ th
           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(3p))
           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 _n_ th 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(3p).
    
           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.
    


* * *