4.4BSD/usr/share/man/cat3/printf.0
PRINTF(3) BSD Programmer's Manual PRINTF(3)
NNAAMMEE
pprriinnttff, ffpprriinnttff, sspprriinnttff, ssnnpprriinnttff, vvpprriinnttff, vvffpprriinnttff,, vvsspprriinnttff,
vvssnnpprriinnttff - formatted output conversion
SSYYNNOOPPSSIISS
##iinncclluuddee <<ssttddiioo..hh>>
_i_n_t
pprriinnttff(_c_o_n_s_t _c_h_a_r _*_f_o_r_m_a_t, _._._.);
_i_n_t
ffpprriinnttff(_F_I_L_E _*_s_t_r_e_a_m, _c_o_n_s_t _c_h_a_r _*_f_o_r_m_a_t, _._._.);
_i_n_t
sspprriinnttff(_c_h_a_r _*_s_t_r, _c_o_n_s_t _c_h_a_r _*_f_o_r_m_a_t, _._._.);
_i_n_t
ssnnpprriinnttff(_c_h_a_r _*_s_t_r, _s_i_z_e___t _s_i_z_e, _c_o_n_s_t _c_h_a_r _*_f_o_r_m_a_t, _._._.);
##iinncclluuddee <<ssttddaarrgg..hh>>
_i_n_t
vvpprriinnttff(_c_o_n_s_t _c_h_a_r _*_f_o_r_m_a_t, _v_a___l_i_s_t _a_p);
_i_n_t
vvffpprriinnttff(_F_I_L_E _*_s_t_r_e_a_m, _c_o_n_s_t _c_h_a_r _*_f_o_r_m_a_t, _v_a___l_i_s_t _a_p);
_i_n_t
vvsspprriinnttff(_c_h_a_r _*_s_t_r, _c_h_a_r _*_f_o_r_m_a_t, _v_a___l_i_s_t _a_p);
_i_n_t
vvssnnpprriinnttff(_c_h_a_r _*_s_t_r, _s_i_z_e___t _s_i_z_e, _c_o_n_s_t _c_h_a_r _*_f_o_r_m_a_t, _v_a___l_i_s_t _a_p);
DDEESSCCRRIIPPTTIIOONN
The pprriinnttff() family of functions produces output according to a _f_o_r_m_a_t as
described below. PPrriinnttff() and vvpprriinnttff() write output to _s_t_d_o_u_t_, the
standard output stream; ffpprriinnttff() and vvffpprriinnttff() write output to the giv-
en output _s_t_r_e_a_m; sspprriinnttff(), ssnnpprriinnttff(), vvsspprriinnttff(), and vvssnnpprriinnttff()
write to the character string _s_t_r. These functions write the output under
the control of a _f_o_r_m_a_t string that specifies how subsequent arguments
(or arguments accessed via the variable-length argument facilities of
stdarg(3)) are converted for output. These functions return the number
of characters printed (not including the trailing `\0' used to end output
to strings). SSnnpprriinnttff() and vvssnnpprriinnttff() will write at most _s_i_z_e-1 of the
characters printed into the output string (the _s_i_z_e'th character then
gets the terminating `\0'); if the return value is greater than or equal
to the _s_i_z_e argument, the string was too short and some of the printed
characters were discarded. SSpprriinnttff() and vvsspprriinnttff() effectively assume
an infinite _s_i_z_e.
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
in sequence:
++oo Zero or more of the following flags:
-- A ## character specifying that the value should be converted to an
``alternate form''. For cc, dd, ii, nn, pp, ss, and uu, conversions,
this option has no effect. For oo conversions, the precision of
the number is increased to force the first character of the out-
put string to a zero (except if a zero value is printed with an
explicit precision of zero). For xx and XX conversions, a non-zero
result has the string `0x' (or `0X' for XX conversions) prepended
to it. For ee, EE, ff, gg, and GG, conversions, the result will al-
ways contain a decimal point, even if no digits follow it (nor-
mally, a decimal point appears in the results of those conver-
sions only if a digit follows). For gg and GG conversions, trail-
ing zeros are not removed from the result as they would otherwise
be.
-- A zero `00' character specifying zero padding. For all conver-
sions except nn, the converted value is padded on the left with
zeros rather than blanks. If a precision is given with a numeric
conversion (Mc d, ii, oo, uu, ii, xx, and XX), the `00' flag is ignored.
-- A negative field width flag `--' indicates the converted value is
to be left adjusted on the field boundary. Except for nn conver-
sions, the converted value is padded on the right with blanks,
rather than on the left with blanks or zeros. A `--' overrides a
`00' if both are given.
-- A space, specifying that a blank should be left before a positive
number produced by a signed conversion (dd, ee, EE, ff, gg, GG, or ii).
-- A `++' character specifying that a sign always be placed before a
number produced by a signed conversion. A `++' overrides a space
if both are used.
++oo 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.
++oo An optional precision, in the form of a period `..' followed by an op-
tional digit string. If the digit string is omitted, the precision
is taken as zero. This gives the minimum number of digits to appear
for dd, ii, oo, uu, xx, and XX conversions, the number of digits to appear
after the decimal-point for ee, EE, and ff conversions, the maximum num-
ber of significant digits for gg and GG conversions, or the maximum
number of characters to be printed from a string for ss conversions.
++oo The optional character hh, specifying that a following dd, ii, oo, uu, xx,
or XX conversion corresponds to a _s_h_o_r_t _i_n_t or _u_n_s_i_g_n_e_d _s_h_o_r_t _i_n_t ar-
gument, or that a following nn conversion corresponds to a pointer to
a _s_h_o_r_t _i_n_t argument.
++oo The optional character ll (ell) specifying that a following dd, ii, oo,
uu, xx, or XX conversion applies to a pointer to a _l_o_n_g _i_n_t or _u_n_s_i_g_n_e_d
_l_o_n_g _i_n_t argument, or that a following nn conversion corresponds to a
pointer to a _l_o_n_g _i_n_t argument.
++oo The optional character qq, specifying that a following dd, ii, oo, uu, xx,
or XX conversion corresponds to a _q_u_a_d _i_n_t or _u_n_s_i_g_n_e_d _q_u_a_d _i_n_t argu-
ment, or that a following nn conversion corresponds to a pointer to a
_q_u_a_d _i_n_t argument.
++oo The character LL specifying that a following ee, EE, ff, gg, or GG conver-
sion corresponds to a _l_o_n_g _d_o_u_b_l_e argument (but note that long double
values are not currently supported by the VAX and Tahoe compilers).
++oo A character that specifies the type of conversion to be applied.
A field width or precision, or both, may be indicated by an asterisk `*'
instead of a digit string. In this case, an _i_n_t 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.
The conversion specifiers and their meanings are:
ddiioouuxxXX The _i_n_t (or appropriate variant) argument is converted to signed
decimal (dd and ii), unsigned octal (oo), unsigned decimal (uu), or
unsigned hexadecimal (xx and XX) notation. The letters aabbccddeeff are
used for xx conversions; the letters AABBCCDDEEFF are used for conver-
sions. 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.
DDOOUU The _l_o_n_g _i_n_t argument is converted to signed decimal, unsigned
octal, or unsigned decimal, as if the format had been lldd, lloo, or
lluu respectively. These conversion characters are deprecated, and
will eventually disappear.
eeEE The _d_o_u_b_l_e argument is rounded and converted in the style
[-]d..dddee+-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 EE con-
version uses the letter EE (rather than ee) to introduce the expo-
nent. The exponent always contains at least two digits; if the
value is zero, the exponent is 00.
ff The _d_o_u_b_l_e 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 _d_o_u_b_l_e argument is converted in style ff or ee (or EE for GG con-
versions). 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 ee 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.
cc The _i_n_t argument is converted to an _u_n_s_i_g_n_e_d _c_h_a_r, and the re-
sulting character is written.
ss The ``_c_h_a_r _*'' argument is expected to be a pointer to an array
of character type (pointer to a string). Characters from the ar-
ray are written up to (but not including) a terminating NUL char-
acter; if a precision is specified, no more than the number spec-
ified 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 The ``_v_o_i_d _*'' pointer argument is printed in hexadecimal (as if
by `%#x' or `%#lx').
nn The number of characters written so far is stored into the inte-
ger indicated by the ``_i_n_t _*'' (or variant) pointer argument. No
argument is converted.
%% A `%' is written. No argument is converted. The complete conver-
sion specification is `%%'.
In no case does a non-existent or small field width cause truncation of a
field; if the result of a conversion is wider than the field width, the
field is expanded to contain the conversion result.
EEXXAAMMPPLLEESS
To print a date and time in the form `Sunday, July 3, 10:02', where
_w_e_e_k_d_a_y and _m_o_n_t_h are pointers to strings:
#include <stdio.h>
fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
To print pi to five decimal places:
#include <math.h>
#include <stdio.h>
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
To allocate a 128 byte string and print into it:
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
char *newfmt(const char *fmt, ...)
{
char *p;
va_list ap;
if ((p = malloc(128)) == NULL)
return (NULL);
va_start(ap, fmt);
(void) vsnprintf(p, 128, fmt, ap);
va_end(ap);
return (p);
}
SSEEEE AALLSSOO
printf(1), scanf(3)
SSTTAANNDDAARRDDSS
The ffpprriinnttff(), pprriinnttff(), sspprriinnttff(), vvpprriinnttff(), vvffpprriinnttff(), and vvsspprriinnttff()
functions conform to ANSI C X3.159-1989 (``ANSI C '').
HHIISSTTOORRYY
The functions ssnnpprriinnttff() and vvssnnpprriinnttff() are new to this release.
BBUUGGSS
The conversion formats %%DD, %%OO, and %%UU are not standard and are provided
only for backward compatibility. The effect of padding the %%pp format
with zeros (either by the `00' flag or by specifying a precision), and the
benign effect (i.e., none) of the `##' flag on %%nn and %%pp conversions, as
well as other nonsensical combinations such as %%LLdd, are not standard;
such combinations should be avoided.
Because sspprriinnttff() and vvsspprriinnttff() assume an infinitely long string,
callers must be careful not to overflow the actual space; this is often
impossible to assure. For safety, programmers should use the ssnnpprriinnttff()
interface instead. Unfortunately, this interface is not portable.
4.4BSD June 4, 1993 4