printf, fprintf, sprintf - formatted output conversion
printf(format [, arg ] ... )
fprintf(stream, format [, arg ] ... )
sprintf(s, format [, arg ] ... )
char *s, format;
_doprnt(format, args, stream)
Printf places output on the standard output stream stdout. Fprintf
places output on the named output stream. Sprintf places `output' in
the string s, followed by the character `\0'. All of these routines
work by calling the internal routine _doprnt, using the variable-length
argument facilities of varargs(3).
Each of these functions converts, formats, and prints its arguments
after the first under control of the first argument. The first argu-
ment is a character string which contains two types of objects: plain
characters, which are simply copied to the output stream, and conver-
sion specifications, each of which causes conversion and printing of
the next successive arg printf.
Each conversion specification is introduced by the character %. Fol-
lowing the %, there may be
o an optional minus sign `-' which specifies left adjustment of
the converted value in the indicated field;
o an optional digit string specifying a field width; if the con-
verted value has fewer characters than the field width it will
be blank-padded on the left (or right, if the left-adjustment
indicator has been given) to make up the field width; if the
field width begins with a zero, zero-padding will be done
instead of blank-padding;
o an optional period `.' which serves to separate the field width
from the next digit string;
o an optional digit string specifying a precision which specifies
the number of digits to appear after the decimal point, for e-
and f-conversion, or the maximum number of characters to be
printed from a string;
o an optional `#' character specifying that the value should be
converted to an ``alternate form''. For c, d, s, and u, conver-
sions, this option has no effect. For o conversions, the preci-
sion of the number is increased to force the first character of
the output string to a zero. For x(X) conversion, a non-zero
result has the string 0x(0X) prepended to it. For e, E, f, g,
and G, conversions, the result will always contain a decimal
point, even if no digits follow the point (normally, a decimal
point only appears in the results of those conversions if a
digit follows the decimal point). For g and G conversions,
trailing zeros are not removed from the result as they would
o the character l specifying that a following d, o, x, or u corre-
sponds to a long integer arg.
o a character which indicates the type of conversion to be
A field width or precision may be `*' instead of a digit string. In
this case an integer arg supplies the field width or precision.
The conversion characters and their meanings are
dox The integer arg is converted to decimal, octal, or hexadecimal
f The float or double arg is converted to decimal notation in the
style `[-]ddd.ddd' where the number of d's after the decimal
point is equal to the precision specification for the argument.
If the precision is missing, 6 digits are given; if the preci-
sion is explicitly 0, no digits and no decimal point are
e The float or double arg is converted in the style
`[-]d.ddde+-dd' where there is one digit before the decimal
point and the number after is equal to the precision specifica-
tion for the argument; when the precision is missing, 6 digits
g The float or double arg is printed in style d, in style f, or in
style e, whichever gives full precision in minimum space.
c The character arg is printed.
s Arg is taken to be a string (character pointer) and characters
from the string are printed until a null character or until the
number of characters indicated by the precision specification is
reached; however if the precision is 0 or missing all characters
up to a null are printed.
u The unsigned integer arg is converted to decimal and printed
(the result will be in the range 0 through MAXUINT, where
MAXUINT equals 4294967295 on a VAX-11 and 65535 on a PDP-11).
% Print a `%'; no argument is converted.
In no case does a non-existent or small field width cause truncation of
a field; padding takes place only if the specified field width exceeds
the actual width. Characters generated by printf are printed by
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 %d, %02d:%02d", weekday, month, day, hour, min);
To print pi to 5 decimals:
printf("pi = %.5f", 4*atan(1.0));
putc(3S), scanf(3S), ecvt(3)
Very wide fields (>128 characters) fail.
1 April 1981 PRINTF(3S)