FWPRINTF
Section: POSIX Programmer's Manual (3P)
Updated: 2017
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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.1-2017 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.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().
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 .