PRINTF(3S-SysV) RISC/os Reference Manual PRINTF(3S-SysV)
NAME
printf, fprintf, sprintf, vprintf, vfprintf, vsprintf -
print formatted output
SYNOPSIS
#include <bsd/sys/types.h>
#include <stdio.h>
#include <varargs.h>
int printf (format , arg ... )
char *format;
int fprintf (stream, format , arg ... )
FILE *stream;
char *format;
int sprintf (s, format [ , arg ] ... )
char *s, *format;
int vprintf (format, ap)
char *format;
va_list ap;
int vfprintf (stream, format, ap)
FILE *stream;
char *format;
va_list ap;
int vsprintf (s, format, ap)
char *s, *format;
va_list 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. Each
function returns the number of characters transmitted (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 charac-
ters, 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.
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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 charac-
ters 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 sig-
nificant digits for the g and G conversion, or the max-
imum 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 -).
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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 meanings are:
d,i,o,u,x,X
The integer arg is converted to signed decimal (d or
i), unsigned octal, (o), decimal (u), or hexadecimal
notation (x or 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.
f The float or double arg is converted to decimal nota-
tion in the style ``[-]ddd.ddd,'' where the number of
digits after the decimal point is equal to the preci-
sion 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,
six 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
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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 preci-
sion. 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 pointer) and
characters from the string are printed until a null
character (\0) is encountered or the number of charac-
ters 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 printing floating point types (float and double), if the
exponent is 0x7FF and the mantissa is not equal to zero,
then the output is
[-]NaN0xdddddddd
where 0xdddddddd is the hexadecimal representation of the
leftmost 32 bits of the mantissa. If the mantissa is zero,
the output is
[+]inf.
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. Characters generated by
printf and fprintf are printed as if putc(3S) had been
called.
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).
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 %i, %d:%.2d", weekday, month, day, hour, min);
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To print pi to 5 decimal places:
printf("pi = %.5f", 4 * atan(1.0));
The following demonstrates the use of vfprintf to write an
error routine.
#include <stdio.h>
#include <varargs.h>
.
.
.
/*
* error should be called like
* error(function_name, format, arg1, arg2...); */
/*VARARGS */
void
error(va_alist)
/* Note that the function_name and format arguments cannot be
* separately declared because of the definition of varargs. */
va_dcl
{
va_list args;
char *fmt;
va_start(args);
/* print out name of function causing error */
(void)fprintf(stderr, "ERROR in %s: ", va_arg(args, char *));
fmt = va_arg(args, char *);
/* print out remainder of message */
(void)vfprintf(stderr, fmt, args);
va_end(args);
(void)abort( );
}
SEE ALSO
ecvt(3C), putc(3S), scanf(3S), stdio(3S).
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