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FWPRINTF(3P) POSIX Programmer's Manual FWPRINTF(3P)
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.
fwprintf, swprintf, wprintf — print formatted wide-character output
#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, ...);
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 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$" form of
conversion specification, numbered arguments in the argument list can
be referenced from the format wide-character string as many times as
required.
In format wide-character strings containing the % form of conversion
specification, each argument in the argument list shall be used
exactly once.
All forms of the fwprintf() function allow for the insertion of a
locale-dependent radix character in the output string, output as a
wide-character value. The radix character is defined in the current
locale (category LC_NUMERIC). In the POSIX locale, or in a locale
where the radix character is not defined, the radix character shall
default to a <period> ('.').
Each conversion specification is introduced by the '%' wide character
or by the wide-character sequence "%n$", 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 increases the precision (if
necessary) to force the first digit of the result to be 0.
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.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 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().
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.
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, all forms of fwprintf() may fail if:
EINVAL There are insufficient arguments.
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.
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
None.
None.
None.
Section 2.5, Standard I/O Streams, btowc(3p), fputwc(3p),
fwscanf(3p), mbrtowc(3p), setlocale(3p)
The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale,
stdio.h(0p), wchar.h(0p)
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 FWPRINTF(3P)
Pages that refer to this page: wchar.h(0p), fwscanf(3p), swprintf(3p), vfwprintf(3p), wprintf(3p)