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

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

SYNOPSIS         top

       #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         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.1‐2017 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 d, i, o, u, x, and X conversion specifiers;
           the number of digits to appear after the radix character for
           the a, A, e, E, f, and F conversion specifiers; the maximum
           number of significant digits for the g and G conversion
           specifiers; or the maximum number of wide characters to be
           printed from a string in the s 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 (%i, %d, %u, %f, %F, %g, or %G) 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 o 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 x or X conversion
               specifiers, a non-zero result shall have 0x (or 0X)
               prefixed to it. For a, A, e, E, f, F, g, and G 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 g and G
               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 d, i, o, u, x, X, a, A, e, E, f, F, g, and G
               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 '0' and '-' flags
               both appear, the '0' flag shall be ignored. For d, i, o,
               u, x, and X conversion specifiers, if a precision is
               specified, the '0' flag shall be ignored.  If the '0' 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 d, i, o, u, x, or X 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 n conversion specifier
               applies to a pointer to a signed char argument.

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

       l (ell) Specifies that a following d, i, o, u, x, or X conversion
               specifier applies to a long or unsigned long argument;
               that a following n conversion specifier applies to a
               pointer to a long argument; that a following c conversion
               specifier applies to a wint_t argument; that a following s
               conversion specifier applies to a pointer to a wchar_t
               argument; or has no effect on a following a, A, e, E, f,
               F, g, or G conversion specifier.

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

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

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

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

       L       Specifies that a following a, A, e, E, f, F, g, or G
               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 x 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 F 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 E 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 f or F conversion specifier.

       g, G    The double argument representing a floating-point number
               shall be converted in the style f or e (or in the style F
               or E in the case of a G conversion specifier), depending
               on the value converted and the precision.  Let P 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
               E would have an exponent of X:

               --  If P>X≥-4, the conversion shall be with style f (or F)
                   and precision P-(X+1).

               --  Otherwise, the conversion shall be with style e (or E)
                   and precision P-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 f or F conversion specifier.

       a, A    A double argument representing a floating-point number
               shall be converted in the style "[-]0xh.hhhhd", 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 a
               conversion and the letters "ABCDEF" for A conversion. The
               A 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 f or F conversion specifier.

       c       If no l (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 l (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 l (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 a and A 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 e, E, f, F, g, and G 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         top

       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         top

       For the conditions under which fwprintf() and wprintf() fail and
       may fail, refer to fputwc(3p).

       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         top

       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         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       Section 2.5, Standard I/O Streams, btowc(3p), fputwc(3p),
       fwscanf(3p), mbrtowc(3p), setlocale(3p)

       The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale,
       inttypes.h(0p), stdio.h(0p), wchar.h(0p)

COPYRIGHT         top

       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(3P)

Pages that refer to this page: wchar.h(0p)fwscanf(3p)swprintf(3p)vfwprintf(3p)wprintf(3p)