FWPRINTF(3P) POSIX Programmer's Manual FWPRINTF(3P)
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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.1-2008
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 com-
posed 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$", where n is a decimal integer in the range
[1,{NL_ARGMAX}], giving the position of the argument in the argument
list. This feature provides for the definition of format wide-character
strings that select arguments in an order appropriate to specific lan-
guages (see the EXAMPLES section).
The format can contain either numbered argument specifications (that
is, "%n$" 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, specify-
ing 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$" form of conver-
sion specification, numbered arguments in the argument list can be ref-
erenced from the format wide-character string as many times as
required.
In format wide-character strings containing the % form of conversion
specification, each argument in the argument list shall be used exactly
once.
All forms of the fwprintf() function allow for the insertion of a
locale-dependent radix character in the output string, output as a
wide-character value. The radix character is defined in the current
locale (category LC_NUMERIC). In the POSIX locale, or in a locale
where the radix character is not defined, the radix character shall
default to a <period> ('.').
Each conversion specification is introduced by the '%' wide character
or by the wide-character sequence "%n$", 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 num-
ber of digits to appear after the radix character for the a, A, e,
E, f, and F conversion specifiers; the maximum number of signifi-
cant digits for the g and G conversion specifiers; or the maximum
number of wide characters to be printed from a string in the s con-
version 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 argu-
ment.
* 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 contain-
ing the "%n$" form of a conversion specification, a field width or pre-
cision may be indicated by the sequence "*m$", where m is a decimal
integer in the range [1,{NL_ARGMAX}] giving the position in the argu-
ment 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 speci-
fied.
<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 neces-
sary) 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 charac-
ter 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 char-
acters 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 spec-
ifier applies to a signed char or unsigned char argument (the
argument will have been promoted according to the integer pro-
motions, but its value shall be converted to signed char or
unsigned char before printing); or that a following n conver-
sion specifier applies to a pointer to a signed char argument.
h Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a short or unsigned short argument (the argu-
ment will have been promoted according to the integer promo-
tions, but its value shall be converted to short or unsigned
short before printing); or that a following n conversion speci-
fier applies to a pointer to a short argument.
l (ell) Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a long or unsigned long argument; that a fol-
lowing 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 spec-
ifier 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 spec-
ifier 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 spec-
ifier 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 spec-
ifier 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 repre-
sented in fewer digits, it shall be expanded with leading
zeros. The default precision shall be 1. The result of convert-
ing zero with an explicit precision of zero shall be no wide
characters.
o The unsigned argument shall be converted to unsigned octal for-
mat 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 convert-
ing 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 mini-
mum 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 hexadeci-
mal 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 dig-
its, it shall be expanded with leading zeros. The default pre-
cision 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", "infin-
ity", 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 preci-
sion; 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 imple-
mentation-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 con-
verted 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 con-
verted 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 frac-
tional portion remaining.
A double argument representing an infinity or NaN shall be con-
verted 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 hexa-
decimal 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 distin-
guish values of type double, except that trailing zeros may be
omitted; if the precision is zero and the '#' flag is not spec-
ified, no decimal-point wide character shall appear. The let-
ters "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 con-
verted 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 con-
taining 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 unde-
fined.
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. Charac-
ters 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 sig-
nificant 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 representa-
tion 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 char-
acter 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 char-
acter 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.
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-charac-
ter 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
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5, Standard I/O Streams, btowc(), fputwc(), fwscanf(), mbr-
towc(), setlocale()
The Base Definitions volume of POSIX.1-2008, Chapter 7, Locale,
<stdio.h>, <wchar.h>
COPYRIGHT
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 Electri-
cal 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.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FWPRINTF(3P)
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