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FWSCANF(3P)               POSIX Programmer's Manual              FWSCANF(3P)

PROLOG         top

       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         top

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

SYNOPSIS         top

       #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         top

       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.1‐2008 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.

       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 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         top

       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 matching failure or conversion, EOF shall be
       returned.  If any error occurs, 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         top

       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         top

       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         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.5, Standard I/O Streams, getwc(3p), fwprintf(3p),
       setlocale(3p), wcstod(3p), wcstol(3p), wcstoul(3p), wcrtomb(3p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale,
       stdio.h(0p), wchar.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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 .

IEEE/The Open Group                 2013                         FWSCANF(3P)