FWPRINTF(3)                POSIX Programmer's Manual               FWPRINTF(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       fwprintf, swprintf, wprintf -- print formatted wide-character output

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

       int fwprintf(FILE *restrict stream, const wchar_t *restrict format, ...);
       int swprintf(wchar_t *restrict ws, size_t _n,
           const wchar_t *restrict format, ...);
       int wprintf(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 fwprintf() function shall place output on the named output stream.
       The wprintf() function shall place output on the standard output stream
       stdout.  The swprintf() function shall place output followed by the
       null wide character in consecutive wide characters starting at *ws; no
       more than _n wide characters shall be written, including a terminating
       null wide character, which is always added (unless _n is zero).

       Each of these functions shall convert, format, and print its arguments
       under control of the format wide-character string. The format is
       composed of zero or more directives: ordinary wide-characters, which
       are simply copied to the output stream, and conversion specifications,
       each of which results in the fetching of zero or more arguments. The
       results are 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}], giving the position of the argument in the argument
       list. This feature provides for the definition of format wide-character
       strings that select arguments in an order appropriate to specific
       languages (see the EXAMPLES section).

       The format can contain either numbered argument specifications (that
       is, "%_n$" and "*_m$"), or unnumbered argument conversion specifications
       (that is, %% and **), but not both. The only exception to this is that %%%%
       can be mixed with the "%_n$" form. The results of mixing numbered and
       unnumbered argument specifications in a format wide-character string
       are undefined. 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 specified in the format wide-
       character string.

       In format wide-character strings containing the "%_n$" form of
       conversion specification, numbered arguments in the argument list can
       be referenced from the format wide-character string as many times as
       required.

       In format wide-character strings containing the %% form of conversion
       specification, each argument in the argument list shall be used exactly
       once. 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().

       All forms of the fwprintf() function allow for the insertion of a
       locale-dependent radix character in the output string, output 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> (''..'').

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

        *  Zero or more flags (in any order), which modify the meaning of the
           conversion specification.

        *  An optional minimum field width.  If the converted value has fewer
           wide characters than the field width, it shall be padded with
           <space> characters by default on the left; it shall be padded on
           the right, if the left-adjustment flag (''--''), described below, is
           given to the field width. The field width takes the form of an
           <asterisk> (''**''), described below, or a decimal integer.

        *  An optional precision that gives the minimum number of digits to
           appear for the dd, ii, oo, uu, xx, and XX conversion specifiers; the
           number of digits to appear after the radix character for the aa, AA,
           ee, EE, ff, and FF conversion specifiers; the maximum number of
           significant digits for the gg and GG conversion specifiers; or the
           maximum number of wide characters to be printed from a string in
           the ss conversion specifiers. The precision takes the form of a
           <period> (''..'')  followed either by an <asterisk> (''**''), described
           below, or an optional decimal digit string, where a null digit
           string is treated as 0. If a precision appears with any other
           conversion wide character, the behavior is undefined.

        *  An optional length modifier that specifies the size of the
           argument.

        *  A conversion specifier wide character that indicates the type of
           conversion to be applied.

       A field width, or precision, or both, may be indicated by an <asterisk>
       (''**'').  In this case an argument of type int supplies the field width
       or precision. Applications shall ensure that arguments specifying field
       width, or precision, or both appear in that order before the argument,
       if any, to be converted. A negative field width is taken as a ''--'' flag
       followed by a positive field width. A negative precision is taken as if
       the precision were omitted.  In format wide-character strings
       containing the "%_n$" form of a conversion specification, a field width
       or precision may be indicated by the sequence "*_m$", where _m is a
       decimal integer in the range [1,{NL_ARGMAX}] giving the position in the
       argument list (after the format argument) of an integer argument
       containing the field width or precision, for example:


           wprintf(L"%1$d:%2$.*3$d:%4$.*3$d\n", hour, min, precision, sec);

       The flag wide characters and their meanings are:

       '       (The <apostrophe>.)  The integer portion of the result of a
               decimal conversion (%%ii, %%dd, %%uu, %%ff, %%FF, %%gg, or %%GG) shall be
               formatted with thousands' grouping wide characters. For other
               conversions, the behavior is undefined. The numeric grouping
               wide character is used.

       -       The result of the conversion shall be left-justified within the
               field.  The conversion shall be right-justified if this flag is
               not specified.

       +       The result of a signed conversion shall always begin with a
               sign (''++'' or ''--'').  The conversion shall begin with a sign only
               when a negative value is converted if this flag is not
               specified.

       <space> If the first wide character of a signed conversion is not a
               sign, or if a signed conversion results in no wide characters,
               a <space> shall be prefixed to the result. This means that if
               the <space> and ''++'' flags both appear, the <space> flag shall
               be ignored.

       #       Specifies that the value is to be converted to an alternative
               form.  For oo conversion, it shall increase the precision, if
               and only if necessary, to force the first digit of the result
               to be zero (if the value and precision are both 0, a single 0
               is printed). For xx or XX conversion specifiers, a non-zero
               result shall have 0x (or 0X) prefixed to it. For aa, AA, ee, EE, ff,
               FF, gg, and GG conversion specifiers, the result shall always
               contain a radix character, even if no digits follow it. Without
               this flag, a radix character appears in the result of these
               conversions only if a digit follows it. For gg and GG conversion
               specifiers, trailing zeros shall not be removed from the result
               as they normally are. For other conversion specifiers, the
               behavior is undefined.

       0       For dd, ii, oo, uu, xx, XX, aa, AA, ee, EE, ff, FF, gg, and GG conversion
               specifiers, leading zeros (following any indication of sign or
               base) are used to pad to the field width rather than performing
               space padding, except when converting an infinity or NaN. If
               the ''00'' and ''--'' flags both appear, the ''00'' flag shall be
               ignored. For dd, ii, oo, uu, xx, and XX conversion specifiers, if a
               precision is specified, the ''00'' flag shall be ignored.  If the
               ''00'' and <apostrophe> flags both appear, the grouping wide
               characters are inserted before zero padding. For other
               conversions, the behavior is undefined.

       The length modifiers and their meanings are:

       hh      Specifies that a following dd, ii, oo, uu, xx, or XX conversion
               specifier applies to a signed char or unsigned char argument
               (the argument will have been promoted according to the integer
               promotions, but its value shall be converted to signed char or
               unsigned char before printing); or that a following nn
               conversion specifier applies to a pointer to a signed char
               argument.

       h       Specifies that a following dd, ii, oo, uu, xx, or XX conversion
               specifier applies to a short or unsigned short argument (the
               argument will have been promoted according to the integer
               promotions, but its value shall be converted to short or
               unsigned short before printing); or that a following nn
               conversion specifier applies to a pointer to a short argument.

       l (ell) Specifies that a following dd, ii, oo, uu, xx, or XX conversion
               specifier applies to a long or unsigned long argument; that a
               following nn conversion specifier applies to a pointer to a long
               argument; that a following cc conversion specifier applies to a
               wint_t argument; that a following ss conversion specifier
               applies to a pointer to a wchar_t argument; or has no effect on
               a following aa, AA, ee, EE, ff, FF, gg, or GG conversion specifier.

       ll (ell-ell)
               Specifies that a following dd, ii, oo, uu, xx, or XX conversion
               specifier applies to a long long or unsigned long long
               argument; or that a following nn conversion specifier applies to
               a pointer to a long long argument.

       j       Specifies that a following dd, ii, oo, uu, xx, or XX conversion
               specifier applies to an intmax_t or uintmax_t argument; or that
               a following nn conversion specifier applies to a pointer to an
               intmax_t argument.

       z       Specifies that a following dd, ii, oo, uu, xx, or XX conversion
               specifier applies to a size_t or the corresponding signed
               integer type argument; or that a following nn conversion
               specifier applies to a pointer to a signed integer type
               corresponding to a size_t argument.

       t       Specifies that a following dd, ii, oo, uu, xx, or XX conversion
               specifier applies to a ptrdiff_t or the corresponding unsigned
               type argument; or that a following nn conversion specifier
               applies to a pointer to a ptrdiff_t argument.

       L       Specifies that a following aa, AA, ee, EE, ff, FF, gg, or GG conversion
               specifier applies to a long double argument.

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

       The conversion specifiers and their meanings are:

       d, i    The int argument shall be converted to a signed decimal in the
               style "[-]dddd". The precision specifies the minimum number of
               digits to appear; if the value being converted can be
               represented in fewer digits, it shall be expanded with leading
               zeros. The default precision shall be 1. The result of
               converting zero with an explicit precision of zero shall be no
               wide characters.

       o       The unsigned argument shall be converted to unsigned octal
               format in the style "dddd".  The precision specifies the
               minimum number of digits to appear; if the value being
               converted can be represented in fewer digits, it shall be
               expanded with leading zeros. The default precision shall be 1.
               The result of converting zero with an explicit precision of
               zero shall be no wide characters.

       u       The unsigned argument shall be converted to unsigned decimal
               format in the style "dddd".  The precision specifies the
               minimum number of digits to appear; if the value being
               converted can be represented in fewer digits, it shall be
               expanded with leading zeros. The default precision shall be 1.
               The result of converting zero with an explicit precision of
               zero shall be no wide characters.

       x       The unsigned argument shall be converted to unsigned
               hexadecimal format in the style "dddd"; the letters "abcdef"
               are used. The precision specifies the minimum number of digits
               to appear; if the value being converted can be represented in
               fewer digits, it shall be expanded with leading zeros. The
               default precision shall be 1. The result of converting zero
               with an explicit precision of zero shall be no wide characters.

       X       Equivalent to the xx conversion specifier, except that letters
               "ABCDEF" are used instead of "abcdef".

       f, F    The double argument shall be converted to decimal notation in
               the style "[-]ddd.ddd", where the number of digits after the
               radix character shall be equal to the precision specification.
               If the precision is missing, it shall be taken as 6; if the
               precision is explicitly zero and no ''##'' flag is present, no
               radix character shall appear. If a radix character appears, at
               least one digit shall appear before it. The value shall be
               rounded in an implementation-defined manner to the appropriate
               number of digits.

               A double argument representing an infinity shall be converted
               in one of the styles "[-]inf" or "[-]infinity"; which style is
               implementation-defined. A double argument representing a NaN
               shall be converted in one of the styles "[-]nan" or "[-]nan(_n_-
               char-sequence)"; which style, and the meaning of any n-char-
               sequence, is implementation-defined. The FF conversion specifier
               produces "INF", "INFINITY", or "NAN" instead of "inf",
               "infinity", or "nan", respectively.

       e, E    The double argument shall be converted in the style
               "[-]d.ddde+-dd", where there shall be one digit before the
               radix character (which is non-zero if the argument is non-zero)
               and the number of digits after it shall be equal to the
               precision; if the precision is missing, it shall be taken as 6;
               if the precision is zero and no ''##'' flag is present, no radix
               character shall appear. The value shall be rounded in an
               implementation-defined manner to the appropriate number of
               digits. The EE conversion wide character shall produce a number
               with 'E' instead of 'e' introducing the exponent. The exponent
               shall always contain at least two digits. If the value is zero,
               the exponent shall be zero.

               A double argument representing an infinity or NaN shall be
               converted in the style of an ff or FF conversion specifier.

       g, G    The double argument representing a floating-point number shall
               be converted in the style ff or ee (or in the style FF or EE in the
               case of a GG conversion specifier), depending on the value
               converted and the precision.  Let PP equal the precision if non-
               zero, 6 if the precision is omitted, or 1 if the precision is
               zero. Then, if a conversion with style EE would have an exponent
               of _X:

               --  If PP>_X>=-4, the conversion shall be with style ff (or FF) and
                   precision PP-(_X+1).

               --  Otherwise, the conversion shall be with style ee (or EE) and
                   precision PP-1.

               Finally, unless the ''##'' flag is used, any trailing zeros shall
               be removed from the fractional portion of the result and the
               decimal-point character shall be removed if there is no
               fractional portion remaining.

               A double argument representing an infinity or NaN shall be
               converted in the style of an ff or FF conversion specifier.

       a, A    A double argument representing a floating-point number shall be
               converted in the style "[-]0x_h.hhhhp+-_d", where there shall be
               one hexadecimal digit (which is non-zero if the argument is a
               normalized floating-point number and is otherwise unspecified)
               before the decimal-point wide character and the number of
               hexadecimal digits after it shall be equal to the precision; if
               the precision is missing and FLT_RADIX is a power of 2, then
               the precision shall be sufficient for an exact representation
               of the value; if the precision is missing and FLT_RADIX is not
               a power of 2, then the precision shall be sufficient to
               distinguish values of type double, except that trailing zeros
               may be omitted; if the precision is zero and the ''##'' flag is
               not specified, no decimal-point wide character shall appear.
               The letters "abcdef" are used for aa conversion and the letters
               "ABCDEF" for AA conversion. The AA conversion specifier produces
               a number with 'X' and 'P' instead of 'x' and 'p'.  The exponent
               shall always contain at least one digit, and only as many more
               digits as necessary to represent the decimal exponent of 2. If
               the value is zero, the exponent shall be zero.

               A double argument representing an infinity or NaN shall be
               converted in the style of an ff or FF conversion specifier.

       c       If no ll (ell) qualifier is present, the int argument shall be
               converted to a wide character as if by calling the btowc()
               function and the resulting wide character shall be written.
               Otherwise, the wint_t argument shall be converted to wchar_t,
               and written.

       s       If no ll (ell) qualifier is present, the application shall
               ensure that the argument is a pointer to a character array
               containing a character sequence beginning in the initial shift
               state. Characters from the array shall be converted as if by
               repeated calls to the mbrtowc() function, with the conversion
               state described by an mbstate_t object initialized to zero
               before the first character is converted, and written up to (but
               not including) the terminating null wide character.  If the
               precision is specified, no more than that many wide characters
               shall be written. If the precision is not specified, or is
               greater than the size of the array, the application shall
               ensure that the array contains a null wide character.

               If an ll (ell) qualifier is present, the application shall
               ensure that the argument is a pointer to an array of type
               wchar_t.  Wide characters from the array shall be written up to
               (but not including) a terminating null wide character. If no
               precision is specified, or is greater than the size of the
               array, the application shall ensure that the array contains a
               null wide character. If a precision is specified, no more than
               that many wide characters shall be written.

       p       The application shall ensure that the argument is a pointer to
               void.  The value of the pointer shall be converted to a
               sequence of printable wide characters in an implementation-
               defined manner.

       n       The application shall ensure that the argument is a pointer to
               an integer into which is written the number of wide characters
               written to the output so far by this call to one of the
               fwprintf() functions. No argument shall be converted, but one
               shall be consumed.  If the conversion specification includes
               any flags, a field width, or a precision, the behavior is
               undefined.

       C       Equivalent to lc.

       S       Equivalent to ls.

       %       Output a ''%%'' wide character; no argument shall be converted.
               The entire conversion specification shall be %%%%.

       If a conversion specification does not match one of the above forms,
       the behavior is undefined.

       In no case does a nonexistent or small field width cause truncation of
       a field; if the result of a conversion is wider than the field width,
       the field shall be expanded to contain the conversion result.
       Characters generated by fwprintf() and wprintf() shall be printed as if
       fputwc() had been called.

       For aa and AA conversions, if FLT_RADIX is not a power of 2 and the
       result is not exactly representable in the given precision, the result
       should be one of the two adjacent numbers in hexadecimal floating style
       with the given precision, with the extra stipulation that the error
       should have a correct sign for the current rounding direction.

       For ee, EE, ff, FF, gg, and GG conversion specifiers, if the number of
       significant decimal digits is at most DECIMAL_DIG, then the result
       should be correctly rounded. If the number of significant decimal
       digits is more than DECIMAL_DIG but the source value is exactly
       representable with DECIMAL_DIG digits, then the result should be an
       exact representation with trailing zeros.  Otherwise, the source value
       is bounded by two adjacent decimal strings _L < _U, both having
       DECIMAL_DIG significant digits; the value of the resultant decimal
       string _D should satisfy _L <= _D <= _U, with the extra stipulation that
       the error should have a correct sign for the current rounding
       direction.

       The last data modification and last file status change timestamps of
       the file shall be marked for update between the call to a successful
       execution of fwprintf() or wprintf() and the next successful completion
       of a call to fflush() or fclose() on the same stream, or a call to
       exit() or abort().

RETURN VALUE
       Upon successful completion, these functions shall return the number of
       wide characters transmitted, excluding the terminating null wide
       character in the case of swprintf(), or a negative value if an output
       error was encountered, and set errno to indicate the error.

       If _n or more wide characters were requested to be written, swprintf()
       shall return a negative value, and set errno to indicate the error.

ERRORS
       For the conditions under which fwprintf() and wprintf() fail and may
       fail, refer to fputwc().

       In addition, all forms of fwprintf() shall fail if:

       EILSEQ A wide-character code that does not correspond to a valid
              character has been detected.

       In addition, fwprintf() and wprintf() may fail if:

       ENOMEM Insufficient storage space is available.

       The swprintf() shall fail if:

       EOVERFLOW
              The value of _n is greater than {INT_MAX} or the number of bytes
              needed to hold the output excluding the terminating null is
              greater than {INT_MAX}.

       The following sections are informative.

EXAMPLES
       To print the language-independent date and time format, the following
       statement could be used:


           wprintf(format, weekday, month, day, hour, min);

       For American usage, format could be a pointer to the wide-character
       string:


           L"%s, %s %d, %d:%.2d\n"

       producing the message:


           Sunday, July 3, 10:02

       whereas for German usage, format could be a pointer to the wide-
       character string:


           L"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"

       producing the message:


           Sonntag, 3. Juli, 10:02

APPLICATION USAGE
       None.

RATIONALE
       If an implementation detects that there are insufficient arguments for
       the format, it is recommended that the function should fail and report
       an [EINVAL] error.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 2.5, Standard I/O Streams, btowc(), fputwc(), fwscanf(),
       mbrtowc(), setlocale()

       The Base Definitions volume of POSIX.1-2017, Chapter _7, Locale,
       <inttypes.h>, <stdio.h>, <wchar.h>

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 .



IEEE/The Open Group                  2017                          FWPRINTF(3)
