printf(3S-BSD) MISC. REFERENCE MANUAL PAGES printf(3S-BSD)
NAME
printf, fprintf, sprintf, vprintf, vfprintf, vsprintf - for-
matted output conversion
SYNOPSIS
cc [ flag... ] file ... -lucb
#include <stdio.h>
int printf(format [ , arg ] ... )
char *format;
int fprintf(stream, format [ , arg ] ... )
FILE *stream;
char *format;
char *sprintf(s, format [ , arg ] ... )
char *s, *format;
int vprintf(format, ap)
char *format;
valist ap;
int vfprintf(stream, format, ap)
FILE *stream;
char *format;
valist ap;
char *vsprintf(s, format, ap)
char *s, *format;
valist ap;
DESCRIPTION
printf places output on the standard output stream stdout.
fprintf places output on the named output stream. sprintf
places ``output,'' followed by the NULL character (\0), in
consecutive bytes starting at *s; it is the user's responsi-
bility to ensure that enough storage is available. vprintf,
vfprintf, and vsprintf are the same as printf, fprintf, and
sprintf respectively, except that instead of being called
with a variable number of arguments, they are called with an
argument list as defined by varargs(5). Each of these func-
tions converts, formats, and prints its args under control
of the format. The format is a character string which con-
tains two types of objects: plain characters, which are
simply copied to the output stream, and conversion specifi-
cations, each of which causes conversion and printing of
zero or more args. The results are undefined if there are
insufficient args for the format. If the format is
exhausted while args remain, the excess args are simply
ignored. Each conversion specification is introduced by the
character %. After the %, the following appear in sequence:
Zero or more flags, which modify the meaning of the
conversion specification. An optional decimal digit
string specifying a minimum field width. If the con-
verted value has fewer characters than the field width,
it will be padded on the left (or right, if the left-
adjustment flag `-', described below, has been given)
to the field width. The padding is with blanks unless
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printf(3S-BSD) MISC. REFERENCE MANUAL PAGES printf(3S-BSD)
the field width digit string starts with a zero, in
which case the padding is with zeros. A precision that
gives the minimum number of digits to appear for the d,
i, o, u, x, or X conversions, the number of digits to
appear after the decimal point for the e, E, and f
conversions, the maximum number of significant digits
for the g and G conversion, or the maximum number of
characters to be printed from a string in s conversion.
The precision takes the form of a period (.) followed
by a decimal digit string; a NULL digit string is
treated as zero. Padding specified by the precision
overrides the padding specified by the field width. An
optional l (ell) specifying that a following d, i, o,
u, x, or X conversion character applies to a long
integer arg. An l before any other conversion charac-
ter is ignored. A character that indicates 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
integer arg supplies the field width or precision. The arg
that is actually converted is not fetched until the conver-
sion letter is seen, so the args specifying field width or
precision must appear before the arg (if any) to be con-
verted. A negative field width argument is taken as a `-'
flag followed by a positive field width. If the precision
argument is negative, it will be changed to zero. The flag
characters and their meanings are:
- The result of the conversion will be left-
justified within the field.
+ The result of a signed conversion will always
begin with a sign (+ or -).
blank If the first character of a signed conversion is
not a sign, a blank will be prefixed to the
result. This implies that if the blank and +
flags both appear, the blank flag will be ignored.
# This flag specifies that the value is to be con-
verted to an ``alternate form.''For c, d, i, s,
and u conversions, the flag has no effect. For o
conversion, it increases the precision to force
the first digit of the result to be a zero. For x
or X conversion, a non-zero result will have 0x or
0X prefixed to it. For e, E, f, g, and G conver-
sions, the result will always contain a decimal
point, even if no digits follow the point (nor-
mally, a decimal point appears in the result of
these conversions only if a digit follows it).
For g and G conversions, trailing zeroes will not
be removed from the result (which they normally
are). The conversion characters and their mean-
ings are:
d,i,o,u,x,X
The integer arg is converted to signed decimal (d
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or i), unsigned octal (o), unsigned decimal (u),
or unsigned hexadecimal notation (x and X),
respectively; the letters abcdef are used for x
conversion and the letters ABCDEF for X conver-
sion. The precision specifies the minimum number
of digits to appear; if the value being converted
can be represented in fewer digits, it will be
expanded with leading zeroes. (For compatibility
with older versions, padding with leading zeroes
may alternatively be specified by prepending a
zero to the field width. This does not imply an
octal value for the field width.) The default
precision is 1. The result of converting a zero
value with a precision of zero is a NULL string.
f The float or double arg is converted to decimal
notation in the style [-]ddd.ddd where the number
of digits after the decimal point is equal to the
precision specification. If the precision is
missing, 6 digits are given; if the precision is
explicitly 0, no digits and no decimal point are
printed.
e,E The float or double arg is converted in the style
[-]d.ddde+ddd, where there is one digit before the
decimal point and the number of digits after it is
equal to the precision; when the precision is
missing, 6 digits are produced; if the precision
is zero, no decimal point appears. The E format
code will produce a number with E instead of e
introducing the exponent. The exponent always
contains at least two digits.
g,G The float or double arg is printed in style f or e
(or in style E in the case of a G format code),
with the precision specifying the number of signi-
ficant digits. The style used depends on the
value converted: style e or E will be used only
if the exponent resulting from the conversion is
less than -4 or greater than the precision.
Trailing zeroes are removed from the result; a
decimal point appears only if it is followed by a
digit. The e, E, f, g, and G formats print IEEE
indeterminate values (infinity or not-a-number) as
``Infinity'' or ``NaN'' respectively.
c The character arg is printed.
s The arg is taken to be a string (character
pointer) and characters from the string are
printed until a NULL character (\0) is encountered
or until the number of characters indicated by the
precision specification is reached. If the preci-
sion is missing, it is taken to be infinite, so
all characters up to the first NULL character are
printed. A NULL value for arg will yield unde-
fined results.
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% Print a %; no argument is converted. In no case
does a non-existent or small field width cause
truncation of a field; if the result of a conver-
sion is wider than the field width, the field is
simply expanded to contain the conversion result.
Padding takes place only if the specified field
width exceeds the actual width. Characters gen-
erated by printf and fprintf are printed as if
putc(3S) had been called.
RETURN VALUE
Upon success, printf and fprintf return the number of char-
acters transmitted, excluding the null character. vprintf
and vfprintf return the number of characters transmitted.
sprintf and vsprintf always return s. If an output error is
encountered, printf, fprint, vprintf, and vfprintf, return
EOF.
EXAMPLE
To print a date and time in the form ``Sunday, July 3,
10:02,'' where weekday and month are pointers to NULL-
terminated strings:
printf("%s, %s %i, %d:%.2d", weekday, month, day, hour, min);
To print pi to 5 decimal places:
printf("pi = %.5f", 4 * atan(1. 0));
SEE ALSO
econvert(3) putc(3S), scanf(3S), varargs(5), vprintf(3S) in
the Programmer's Reference Manual.
NOTES
Very wide fields (>128 characters) fail.
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