libc/stdio/wprintf.3

.\"	$OpenBSD: wprintf.3,v 1.8 2019/08/30 20:27:25 jmc Exp $
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.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
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.\"     @(#)printf.3	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: August 30 2019 $
.Dt WPRINTF 3
.Os
.Sh NAME
.Nm wprintf , fwprintf , swprintf ,
.Nm vwprintf , vfwprintf , vswprintf
.Nd formatted wide character output conversion
.Sh SYNOPSIS
.In stdio.h
.In wchar.h
.Ft int
.Fo fwprintf
.Fa "FILE * restrict stream"
.Fa "const wchar_t * restrict format"
.Fa ...
.Fc
.Ft int
.Fo swprintf
.Fa "wchar_t * restrict ws"
.Fa "size_t n"
.Fa "const wchar_t * restrict format"
.Fa ...
.Fc
.Ft int
.Fo wprintf
.Fa "const wchar_t * restrict format"
.Fa ...
.Fc
.In stdarg.h
.Ft int
.Fo vfwprintf
.Fa "FILE * restrict stream"
.Fa "const wchar_t * restrict format"
.Fa "va_list ap"
.Fc
.Ft int
.Fo vswprintf
.Fa "wchar_t * restrict ws"
.Fa "size_t n"
.Fa "const wchar_t * restrict format"
.Fa "va_list ap"
.Fc
.Ft int
.Fo vwprintf
.Fa "const wchar_t * restrict format"
.Fa "va_list ap"
.Fc
.Sh DESCRIPTION
The
.Fn wprintf
family of functions produces output according to a
.Fa format
as described below.
The
.Fn wprintf
and
.Fn vwprintf
functions
write output to
.Dv stdout ,
the standard output stream;
.Fn fwprintf
and
.Fn vfwprintf
write output to the given output
.Fa stream ;
.Fn swprintf
and
.Fn vswprintf
write to the wide character string
.Fa ws .
.Pp
These functions write the output under the control of a
.Fa format
string that specifies how subsequent arguments
(or arguments accessed via the variable-length argument facilities of
.Xr va_start 3 )
are converted for output.
.Pp
These functions return the number of characters printed
(not including the trailing
.Ql \e0
used to end output to strings).
.Pp
The
.Fn swprintf
and
.Fn vswprintf
functions will fail if
.Fa n
or more wide characters were requested to be written,
.Pp
The format string is composed of zero or more directives:
ordinary
characters (not
.Cm % ) ,
which are copied unchanged to the output stream;
and conversion specifications, each of which results
in fetching zero or more subsequent arguments.
Each conversion specification is introduced by
the
.Cm %
character.
The arguments must correspond properly (after type promotion)
with the conversion specifier.
After the
.Cm % ,
the following appear in sequence:
.Bl -bullet
.It
An optional field, consisting of a decimal digit string followed by a
.Cm $ ,
specifying the next argument to access.
If this field is not provided, the argument following the last
argument accessed will be used.
Arguments are numbered starting at
.Cm 1 .
If unaccessed arguments in the format string are interspersed with ones that
are accessed the results will be indeterminate.
.It
Zero or more of the following flags:
.Bl -tag -width "'0' (space)"
.It Sq Cm #
The value should be converted to an
.Dq alternate form .
For
.Cm o
conversions, the precision of the number is increased to force the first
character of the output string to a zero (except if a zero value is printed
with an explicit precision of zero).
For
.Cm x
and
.Cm X
conversions, a non-zero result has the string
.Ql 0x
(or
.Ql 0X
for
.Cm X
conversions) prepended to it.
For
.Cm a , A , e , E , f , F , g ,
and
.Cm G
conversions, the result will always contain a decimal point, even if no
digits follow it (normally, a decimal point appears in the results of
those conversions only if a digit follows).
For
.Cm g
and
.Cm G
conversions, trailing zeros are not removed from the result as they
would otherwise be.
For all other formats, behaviour is undefined.
.It So Cm 0 Sc (zero)
Zero padding.
For all conversions except
.Cm n ,
the converted value is padded on the left with zeros rather than blanks.
If a precision is given with a numeric conversion
.Cm ( d , i , o , u , i , x ,
and
.Cm X ) ,
the
.Cm 0
flag is ignored.
.It Sq Cm \-
A negative field width flag;
the converted value is to be left adjusted on the field boundary.
Except for
.Cm n
conversions, the converted value is padded on the right with blanks,
rather than on the left with blanks or zeros.
A
.Cm \-
overrides a
.Cm 0
if both are given.
.It So "\ " Sc (space)
A blank should be left before a positive number
produced by a signed conversion
.Cm ( a , A , d , e , E , f , F , g , G ,
or
.Cm i ) .
.It Sq Cm +
A sign must always be placed before a
number produced by a signed conversion.
A
.Cm +
overrides a space if both are used.
.It Sq Cm '
On
.Ox ,
this flag has no effect.
On other systems, it may cause the insertion of
.Xr locale 1 Ns -dependent
thousands separator characters into the integral parts of arguments
of the
.Cm d , i , u , f ,
or
.Cm F
conversions.
.El
.It
An optional decimal digit string specifying a minimum field width.
If the converted value has fewer characters than the field width, it will
be padded with spaces on the left (or right, if the left-adjustment
flag has been given) to fill out
the field width.
.It
An optional precision, in the form of a period
.Cm \&.
followed by an
optional digit string.
If the digit string is omitted, the precision is taken as zero.
This gives the minimum number of digits to appear for
.Cm d , i , o , u , x ,
and
.Cm X
conversions, the number of digits to appear after the decimal-point for
.Cm a , A , e , E , f ,
and
.Cm F
conversions, the maximum number of significant digits for
.Cm g
and
.Cm G
conversions, or the maximum number of characters to be printed from a
string for
.Cm s
conversions.
.It
An optional length modifier that specifies the size of the argument.
The following length modifiers are valid for the
.Cm d , i , n , o , u , x ,
or
.Cm X
conversion:
.Bl -column "q (deprecated)" "signed char" "unsigned long long" "long long *"
.It Sy Modifier Ta Sy "d, i" Ta Sy "o, u, x, X" Ta Sy n
.It hh Ta "signed char" Ta "unsigned char" Ta "signed char *"
.It h Ta short Ta "unsigned short" Ta "short *"
.It "l (ell)" Ta long Ta "unsigned long" Ta "long *"
.It "ll (ell ell)" Ta "long long" Ta "unsigned long long" Ta "long long *"
.It j Ta intmax_t Ta uintmax_t Ta "intmax_t *"
.It t Ta ptrdiff_t Ta (see note) Ta "ptrdiff_t *"
.It z Ta "(see note)" Ta size_t Ta "(see note)"
.It "q (deprecated)" Ta quad_t Ta u_quad_t Ta "quad_t *"
.El
.Pp
Note:
the
.Cm t
modifier, when applied to a
.Cm o , u , x ,
or
.Cm X
conversion, indicates that the argument is of an unsigned type
equivalent in size to a
.Vt ptrdiff_t .
The
.Cm z
modifier, when applied to a
.Cm d
or
.Cm i
conversion, indicates that the argument is of a signed type equivalent in
size to a
.Vt size_t .
Similarly, when applied to an
.Cm n
conversion, it indicates that the argument is a pointer to a signed type
equivalent in size to a
.Vt size_t .
.Pp
The following length modifier is valid for the
.Cm a , A , e , E , f , F , g ,
or
.Cm G
conversion:
.Bl -column "Modifier" "a, A, e, E, f, F, g, G"
.It Sy Modifier Ta Cm "a,A,e,E,f,F,g,G"
.It Cm L Ta Vt "long double"
.El
.Pp
The following length modifier is valid for the
.Cm c
or
.Cm s
conversion:
.Bl -column "Modifier" "wint_t" "wchar_t *"
.It Sy Modifier Ta Cm c Ta Cm s
.It Cm l No (ell) Ta Vt wint_t Ta Vt "wchar_t *"
.El
.It
A character that specifies the type of conversion to be applied.
.El
.Pp
A field width or precision, or both, may be indicated by
an asterisk
.Ql *
or an asterisk followed by one or more decimal digits and a
.Ql $
instead of a
digit string.
In this case, an
.Vt int
argument supplies the field width or precision.
A negative field width is treated as a left adjustment flag followed by a
positive field width; a negative precision is treated as though it were
missing.
If a single format directive mixes positional
.Pq Li nn$
and non-positional arguments, the results are undefined.
.Pp
The conversion specifiers and their meanings are:
.Bl -tag -width "diouxX"
.It Cm diouxX
The
.Vt int
(or appropriate variant) argument is converted to signed decimal
.Cm ( d
and
.Cm i ) ,
unsigned octal
.Pq Cm o ,
unsigned decimal
.Pq Cm u ,
or unsigned hexadecimal
.Cm ( x
and
.Cm X )
notation.
The letters
.Dq Li abcdef
are used for
.Cm x
conversions; the letters
.Dq Li ABCDEF
are used for
.Cm X
conversions.
The precision, if any, gives the minimum number of digits that must
appear; if the converted value requires fewer digits, it is padded on
the left with zeros.
.It Cm DOU
The
.Vt "long int"
argument is converted to signed decimal, unsigned octal, or unsigned
decimal, as if the format had been
.Cm ld , lo ,
or
.Cm lu
respectively.
These conversion characters are deprecated, and will eventually disappear.
.It Cm eE
The
.Vt double
argument is rounded and converted in the style
.Sm off
.Oo \- Oc Ar d Li \&. Ar ddd Li e \(+- Ar dd
.Sm on
where there is one digit before the
decimal-point character
and the number of digits after it is equal to the precision;
if the precision is missing,
it is taken as 6; if the precision is
zero, no decimal-point character appears.
An
.Cm E
conversion uses the letter
.Ql E
(rather than
.Ql e )
to introduce the exponent.
The exponent always contains at least two digits; if the value is zero,
the exponent is 00.
.Pp
For
.Cm a , A , e , E , f , F , g ,
and
.Cm G
conversions, positive and negative infinity are represented as
.Li inf
and
.Li -inf
respectively when using the lowercase conversion character, and
.Li INF
and
.Li -INF
respectively when using the uppercase conversion character.
Similarly, NaN is represented as
.Li nan
when using the lowercase conversion, and
.Li NAN
when using the uppercase conversion.
.It Cm fF
The
.Vt double
argument is rounded and converted to decimal notation in the style
.Sm off
.Oo \- Oc Ar ddd Li \&. Ar ddd ,
.Sm on
where the number of digits after the decimal-point character
is equal to the precision specification.
If the precision is missing, it is taken as 6; if the precision is
explicitly zero, no decimal-point character appears.
If a decimal point appears, at least one digit appears before it.
.It Cm gG
The
.Vt double
argument is converted in style
.Cm f
or
.Cm e
(or
.Cm F
or
.Cm E
for
.Cm G
conversions).
The precision specifies the number of significant digits.
If the precision is missing, 6 digits are given; if the precision is zero,
it is treated as 1.
Style
.Cm e
is used if the exponent from its conversion is less than \-4 or greater than
or equal to the precision.
Trailing zeros are removed from the fractional part of the result; a
decimal point appears only if it is followed by at least one digit.
.It Cm aA
The
.Vt double
argument is converted to hexadecimal notation in the style
.Sm off
.Oo \- Oc Li 0x Ar h Li \&. Ar hhhp Oo \(+- Oc Ar d ,
.Sm on
where the number of digits after the hexadecimal-point character
is equal to the precision specification.
If the precision is missing, it is taken as enough to exactly
represent the floating-point number; if the precision is
explicitly zero, no hexadecimal-point character appears.
This is an exact conversion of the mantissa+exponent internal
floating point representation; the
.Sm off
.Oo \- Oc Li 0x Ar h Li \&. Ar hhh
.Sm on
portion represents exactly the mantissa; only denormalized
mantissas have a zero value to the left of the hexadecimal
point.
The
.Cm p
is a literal character
.Ql p ;
the exponent is preceded by a positive or negative sign
and is represented in decimal, using only enough characters
to represent the exponent.
The
.Cm A
conversion uses the prefix
.Dq Li 0X
(rather than
.Dq Li 0x ) ,
the letters
.Dq Li ABCDEF
(rather than
.Dq Li abcdef )
to represent the hex digits, and the letter
.Ql P
(rather than
.Ql p )
to separate the mantissa and exponent.
.It Cm c
The
.Vt int
argument is converted to an
.Vt "unsigned char" ,
then to a
.Vt wchar_t
as if by
.Xr btowc 3 ,
and the resulting character is written.
.Pp
If the
.Cm l
(ell) modifier is used, the
.Vt wint_t
argument is converted to a
.Vt wchar_t
and written.
.It Cm s
The
.Vt "char *"
argument is expected to be a pointer to an array of character type (pointer
to a string) containing a multibyte sequence.
Characters from the array are converted to wide characters and written up to
(but not including)
a terminating NUL character;
if a precision is specified, no more than the number specified are
written.
If a precision is given, no null character
need be present; if the precision is not specified, or is greater than
the size of the array, the array must contain a terminating NUL character.
.Pp
If the
.Cm l
(ell) modifier is used, the
.Vt "wchar_t *"
argument is expected to be a pointer to an array of wide characters
(pointer to a wide string).
Each wide character in the string
is written.
Wide characters from the array are written up to (but not including)
a terminating wide NUL character;
if a precision is specified, no more than the number specified are
written (including shift sequences).
If a precision is given, no null character
need be present; if the precision is not specified, or is greater than
the number of characters in
the string, the array must contain a terminating wide NUL character.
.It Cm p
The
.Vt "void *"
pointer argument is printed in hexadecimal (as if by
.Ql %#x
or
.Ql %#lx ) .
.It Cm n
The number of characters written so far is stored into the
integer indicated by the
.Vt "int *"
(or variant) pointer argument.
No argument is converted.
.It Cm %
A
.Ql %
is written.
No argument is converted.
The complete conversion specification
is
.Ql %% .
.El
.Pp
In no case does a non-existent or small field width cause truncation of
a numeric field; if the result of a conversion is wider than the field
width, the
field is expanded to contain the conversion result.
.Sh SEE ALSO
.Xr btowc 3 ,
.Xr fputws 3 ,
.Xr printf 3 ,
.Xr putwc 3 ,
.Xr setlocale 3 ,
.Xr wcsrtombs 3
.Sh STANDARDS
The
.Fn wprintf ,
.Fn fwprintf ,
.Fn swprintf ,
.Fn vwprintf ,
.Fn vfwprintf
and
.Fn vswprintf
functions
conform to
.St -isoC-99 .
.Sh CAVEATS
On systems other than
.Ox ,
the
.Dv LC_NUMERIC
.Xr locale 1
category can cause erratic output; see CAVEATS in
.Xr setlocale 3
for details.