PRINTF(S) XENIX System V PRINTF(S)
Name
printf, fprintf, sprintf - Formats output.
Syntax
#include <stdio.h>
int printf (format [ , arg ] ... )
char *format;
int fprintf (stream, format [ , arg ] ... )
FILE *stream;
char *format;
int sprintf (s, format [ , arg ] ... )
char *s, *format;
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 function returns the number of characters placed (not
including the \0 in the case of sprintf), or a negative
value if an output error was encountered.
Each of these functions converts, formats, and prints its
args under control of the format. The format is a character
string that contains two types of objects: plain characters,
which are simply copied to the output stream, and conversion
specifications, each of which results in fetching 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 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. If
the field width is preceded with a ``0'' (e.g., %04),
the converted value will be padded with zeroes. If the
width is preceded with a blank (e.g., % 4), the value
will be preceded with blanks. Padding with zeroes may
be applied to numeric conversions only. Strings and
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characters cannot be zero padded.
A precision that gives the minimum number of digits to
appear for the d, o, u, x, or X conversions, the number
of digits to appear after the decimal point for the e
and f conversions, the maximum number of significant
digits for the 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.
An optional l specifying that a following d, o, u, x,
or X conversion character applies to a long integer
arg.
A character that indicates the type of conversion to be
applied.
A field width or precision 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.
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 prepended 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, 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
(X) conversion, a nonzero result will have 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 appears in the result
of these conversions only if a digit follows it).
For g and G conversions, trailing zeroes will not
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be removed from the result (which they normally
are).
The conversion characters and their meanings are:
d,o,u,x,X The integer arg is converted to signed decimal
(d), unsigned octal (o), unsigned decimal (u), or
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. The default precision is 1. The result
of converting a zero value with a precision of
zero is a null string (unless the conversion is o,
x, or X and the # flag is present).
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, six digits are output; if the
precision is explicitly 0, no decimal point
appears.
e,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 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 exactly two digits. However, if
the value to be printed is greater than or equal
to 1E+100, additional exponent digits will be
pointed as necessary.
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 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.
c The character arg is printed.
s The arg is taken to be a string (character
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pointer) and characters from the string are
printed until a null character (\0) is encountered
or 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.
% Print a %; no argument is converted.
In no case does a nonexistent 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. Characters generated by
printf and fprintf are printed as if putchar had been called
(see putc(S)).
Examples
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, %.2d:%.2d", weekday, month, day,
hour, min);
To print pi to five decimal places:
printf("pi = %.5f", 4*atan(1.0));
See Also
ecvt(S), putc(S), scanf(S)
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