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().
