WPRINTF(3) BSD Library Functions Manual WPRINTF(3)NAME
wprintf, fwprintf, swprintf, vwprintf, vfwprintf, vswprintf — formatted
wide character output conversion
Standard C Library (libc, -lc)
fwprintf(FILE * restrict stream, const wchar_t * restrict format, ...);
swprintf(wchar_t * restrict ws, size_t n,
const wchar_t * restrict format, ...);
wprintf(const wchar_t * restrict format, ...);
vfwprintf(FILE * restrict stream, const wchar_t * restrict, va_list ap);
vswprintf(wchar_t * restrict ws, size_t n,
const wchar_t *restrict format, va_list ap);
vwprintf(const wchar_t * restrict format, va_list ap);
The wprintf() family of functions produces output according to a format
as described below. The wprintf() and vwprintf() functions write output
to stdout, the standard output stream; fwprintf() and vfwprintf() write
output to the given output stream; swprintf() and vswprintf() write to
the wide character string ws.
These functions write the output under the control of a format string
that specifies how subsequent arguments (or arguments accessed via the
variable-length argument facilities of stdarg(3)) are converted for out‐
These functions return the number of characters printed (not including
the trailing ‘\0’ used to end output to strings).
The swprintf() and vswprintf() functions will fail if n or more wide
characters were requested to be written,
The format string is composed of zero or more directives: ordinary char‐
acters (not %), which are copied unchanged to the output stream; and con‐
version specifications, each of which results in fetching zero or more
subsequent arguments. Each conversion specification is introduced by the
% character. The arguments must correspond properly (after type promo‐
tion) with the conversion specifier. After the %, the following appear
· An optional field, consisting of a decimal digit string followed by a
$, specifying the next argument to access. If this field is not pro‐
vided, the argument following the last argument accessed will be
used. Arguments are numbered starting at 1. If unaccessed arguments
in the format string are interspersed with ones that are accessed the
results will be indeterminate.
· Zero or more of the following flags:
‘#’ The value should be converted to an “alternate form”.
For c, d, i, n, p, s, and u conversions, this option has
no effect. For o conversions, the precision of the num‐
ber 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 x and
X conversions, a non-zero result has the string ‘0x’ (or
‘0X’ for X conversions) prepended to it. For a, A, e,
E, f, F, g, and 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 g and G
conversions, trailing zeros are not removed from the
result as they would otherwise be.
‘0’ (zero) Zero padding. For all conversions except n, the con‐
verted value is padded on the left with zeros rather
than blanks. If a precision is given with a numeric
conversion (d, i, o, u, i, x, and X), the 0 flag is
‘-’ A negative field width flag; the converted value is to
be left adjusted on the field boundary. Except for n
conversions, the converted value is padded on the right
with blanks, rather than on the left with blanks or
zeros. A - overrides a 0 if both are given.
‘ ’ (space) A blank should be left before a positive number produced
by a signed conversion (a, A, d, e, E, f, F, g, G, or
‘+’ A sign must always be placed before a number produced by
a signed conversion. A + overrides a space if both are
‘'’ Decimal conversions (d, u, or i) or the integral portion
of a floating point conversion (f or F) should be
grouped and separated by thousands using the non-mone‐
tary separator returned by localeconv(3).
· 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-adjust‐
ment flag has been given) to fill out the field width.
· An optional precision, in the form of a period . 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 d, i, o, u, x, and X conversions, the number of digits to appear
after the decimal-point for a, A, e, E, f, and F conversions, the
maximum number of significant digits for g and G conversions, or the
maximum number of characters to be printed from a string for s con‐
· An optional length modifier, that specifies the size of the argument.
The following length modifiers are valid for the d, i, n, o, u, x, or
Modifier d, i o, u, x, X n
hh signed char unsigned char signed char *
h short unsigned short short *
l (ell) long unsigned long long *
ll (ell ell) long long unsigned long long long long *
j intmax_t uintmax_t intmax_t *
t ptrdiff_t (see note) ptrdiff_t *
z (see note) size_t (see note)
q (deprecated) quad_t u_quad_t quad_t *
Note: the t modifier, when applied to a o, u, x, or X conversion,
indicates that the argument is of an unsigned type equivalent in size
to a ptrdiff_t. The z modifier, when applied to a d or i conversion,
indicates that the argument is of a signed type equivalent in size to
a size_t. Similarly, when applied to an n conversion, it indicates
that the argument is a pointer to a signed type equivalent in size to
The following length modifier is valid for the a, A, e, E, f, F, g,
or G conversion:
Modifier a, A, e, E, f, F, g, G
L long double
The following length modifier is valid for the c or s conversion:
Modifier c s
l (ell) wint_t wchar_t *
· A character that specifies the type of conversion to be applied.
A field width or precision, or both, may be indicated by an asterisk ‘*’
or an asterisk followed by one or more decimal digits and a ‘$’ instead
of a digit string. In this case, an int argument supplies the field
width or precision. A negative field width is treated as a left adjust‐
ment flag followed by a positive field width; a negative precision is
treated as though it were missing. If a single format directive mixes
positional (nn$) and non-positional arguments, the results are undefined.
The conversion specifiers and their meanings are:
diouxX The int (or appropriate variant) argument is converted to signed
decimal (d and i), unsigned octal (o), unsigned decimal (u), or
unsigned hexadecimal (x and X) notation. The letters “abcdef”
are used for x conversions; the letters “ABCDEF” are used for 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.
DOU The long int argument is converted to signed decimal, unsigned
octal, or unsigned decimal, as if the format had been ld, lo, or
lu respectively. These conversion characters are deprecated, and
will eventually disappear.
eE The double argument is rounded and converted in the style
[-]d.ddde±dd where there is one digit before the decimal-point
character and the number of digits after it is equal to the pre‐
cision; if the precision is missing, it is taken as 6; if the
precision is zero, no decimal-point character appears. An E con‐
version uses the letter ‘E’ (rather than ‘e’) to introduce the
exponent. The exponent always contains at least two digits; if
the value is zero, the exponent is 00.
For a, A, e, E, f, F, g, and G conversions, positive and negative
infinity are represented as inf and -inf respectively when using
the lowercase conversion character, and INF and -INF respectively
when using the uppercase conversion character. Similarly, NaN is
represented as nan when using the lowercase conversion, and NAN
when using the uppercase conversion.
fF The double argument is rounded and converted to decimal notation
in the style [-]ddd.ddd, 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.
gG The double argument is converted in style f or e (or F or E for 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 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.
aA The double argument is converted to hexadecimal notation in the
style [-]0xh.hhhp[±]d, where the number of digits after the hexa‐
decimal-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 explic‐
itly zero, no hexadecimal-point character appears. This is an
exact conversion of the mantissa+exponent internal floating point
representation; the [-]0xh.hhh portion represents exactly the
mantissa; only denormalized mantissas have a zero value to the
left of the hexadecimal point. The p is a literal character ‘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 A conversion uses the prefix “0X” (rather than
“0x”), the letters “ABCDEF” (rather than “abcdef”) to represent
the hex digits, and the letter ‘P’ (rather than ‘p’) to separate
the mantissa and exponent.
C Treated as c with the l (ell) modifier.
c The int argument is converted to an unsigned char, then to a
wchar_t as if by btowc(3), and the resulting character is writ‐
If the l (ell) modifier is used, the wint_t argument is converted
to a wchar_t and written.
S Treated as s with the l (ell) modifier.
s The 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 char‐
acters 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 charac‐
ter need be present; if the precision is not specified, or is
greater than the size of the array, the array must contain a ter‐
minating NUL character.
If the l (ell) modifier is used, the 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 includ‐
ing) a terminating wide NUL character; if a precision is speci‐
fied, 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 con‐
tain a terminating wide NUL character.
p The void * pointer argument is printed in hexadecimal (as if by
‘%#x’ or ‘%#lx’).
n The number of characters written so far is stored into the inte‐
ger indicated by the int * (or variant) pointer argument. No
argument is converted.
% A ‘%’ is written. No argument is converted. The complete con‐
version specification is ‘%%’.
The decimal point character is defined in the program's locale (category
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.
Refer to printf(3).
SEE ALSObtowc(3), fputws(3), printf(3), putwc(3), setlocale(3), wcsrtombs(3),
Subject to the caveats noted in the BUGS section of printf(3), the
wprintf(), fwprintf(), swprintf(), vwprintf(), vfwprintf() and
vswprintf() functions conform to ISO/IEC 9899:1999 (“ISO C99”).
BSD July 5, 2003 BSD