printf(3S) (BSD Compatibility Package) printf(3S)
NAME
printf, fprintf, sprintf, vprintf, vfprintf, vsprintf - formatted
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 responsibility 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 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.
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printf(3S) (BSD Compatibility Package) printf(3S)
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 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.
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printf(3S) (BSD Compatibility Package) printf(3S)
# 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,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 and X), respectively; the letters
abcdef are used for x 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.
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printf(3S) (BSD Compatibility Package) printf(3S)
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.
% 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.
RETURN VALUE
Upon success, printf and fprintf return the number of characters
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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