Manual page for PRINTF(3V)
printf, fprintf, sprintf - formatted output conversion
SYNOPSIS
#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;
SYSTEM V SYNOPSIS
The routines above are available as shown, except:
int sprintf(s, format [ , arg... ] )
char *s, *format;
The following are provided for
XPG2
compatibility:
#define nl_printf printf
#define nl_fprintf fprintf
#define nl_sprintf sprintf
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 responsibility to ensure that
enough storage is available.
Each of these functions converts, formats, and prints its
args
under control of the
format.
The
format
is a character string which contains
two types of objects:
plain characters, which are simply copied
to the output stream, and
conversion specifications, 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 either the
%
character or by the character sequence
%digit$,
after which 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 converted 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 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 character 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 conversion letter is seen, so the
args
specifying field width or precision must appear
before
the
arg
(if any) to be converted.
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 converted
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
conversions, the result will always
contain a decimal point,
even if no digits follow the point (normally,
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 meanings are:
- d,i,o,p,u,x,X
-
The integer
arg
is converted to signed decimal
(d
or
i),
unsigned octal
(o),
unsigned decimal
(u),
or unsigned hexadecimal notation
(x,
p,
and
X),
respectively; the letters
abcdef
are used for
x
and
p
conversion and the letters
ABCDEF
for
X
conversion.
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 significant 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 precision 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 undefined results.
- n
-
The argument
arg
is a pointer to an integer into which
is written the number of characters written to the output
so far by this call to one of the
printf()
functions.
No argument is converted.
- %
-
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 conversion 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 generated by
printf()
and
fprintf()
are printed as if
putc.3s
had been called.
All forms of the
printf()
functions allow for the insertion of a language dependent radix character in
the output string.
The radix character is defined by the program's locale (category
LC_NUMERIC).
In the
"C"
locale, or in a locale where the radix character is not defined,
the radix character defaults to
`.'.
Conversions can be applied to the
nth
argument in the argument list, rather than the next unused argument.
In this case, the conversion character
%
is replaced by the sequence
%digit$,
where
digit
is a decimal integer
n
in the range [1,9],
giving the position of the argument in the argument list.
This feature provides for the definition of format strings that
select arguments in an order appropriate to specific languages.
In format strings containing the
%digit$
form of a conversion specification, a field
width or precision may be indicated by the sequence
*digit$,
where
digit
is a decimal integer in the range [1,9] giving the position in the
argument list of an integer
arg
containing the field width or precision.
The
format string
can contain either numbered argument specifications (that is,
%digit$
and
*digit$),
or unnumbered argument specifications (that is
%
and
*),
but not both. The
results of mixing numbered and unnumbered specifications is undefined.
When numbered argument specifications are used,
specifying the
nth
argument requires that all the leading arguments, from the first to the
(n-1)th
be specified in the format string.
SYSTEM V DESCRIPTION
XPG2
requires that
nl_printf,
nl_fprintf
and
nl_sprintf
be defined as
printf,
fprintf
and
sprintf,
respectively
for backward compatibility
RETURN VALUES
On success,
printf()
and
fprintf()
return
the number of characters transmitted, excluding the null character.
On failure,
they return
EOF.
sprintf()
returns
s.
SYSTEM V RETURN VALUES
On success,
sprintf()
returns
the number of characters transmitted, excluding the null character.
On failure,
it returns
EOF.
EXAMPLES
-
printf(format, weekday, month, day, hour, min);
In American usage,
format
could be a pointer to the string:
-
"%s, %s %d, %d:%.2d\n"
producing the message:
-
Sunday, July 3,10:02
Whereas for German usage,
format
could be a pointer to the string:
-
"%1$s, %3$d.%2$s,%4$d:%5$.2d\n"
producing the message:
-
Sonntag, 3.Juli,10:02
To print
\(*p
to 5 decimal places:
-
printf("pi = %.5f", 4 * atan(1. 0));
SEE ALSO
econvert.3
putc.3s
scanf.3v
setlocale.3v
varargs.3
vprintf.3v
BUGS
Very wide fields (>128 characters) fail.
Created by unroff & hp-tools.
© somebody (See intro for details). All Rights Reserved.
Last modified 11/5/97