PRINTF(3)PRINTF(3)NAME
fprintf, printf, sprintf, vprintf, vfprintf, vsprintf - formatted out‐
put conversion
SYNOPSIS
#include <stdio.h>
printf(format [, arg ] ... )
char *format;
fprintf(stream, format [, arg ] ... )
FILE *stream;
char *format;
sprintf(s, format [, arg ] ... )
char *s, *format;
#include <varargs.h>
vprintf(format, args)
char *format;
va_list args;
vfprintf(stream, format, args)
FILE *stream;
char *format;
va_list args;
vsprintf(s, format, args)
char *s, *format;
va_list args;
DESCRIPTION
Printf and vprintf place output on the standard output stream stdout.
Fprintf and vfprintf place output on the named output stream. Sprintf
and vsprintf copy into the string s, followed by the character `\0'.
Printf, fprintf, and sprintf take variadic argument lists directly,
while vprintf, vfprintf, and vsprintf use the variable-length argument
facilities of varargs(3) and hence may be called indirectly (see exam‐
ples).
Each function converts, formats, and prints its arguments after the
format under control of the format argument; each returns the the total
number of characters printed (not including the trailing `\0' in
sprintf and vsprintf). Format is a character string which contains two
types of objects: plain characters, which are simply copied to the out‐
put stream, and conversion specifications, each of which causes conver‐
sion and printing of the next successive arg.
Each conversion specification is introduced by the percent character
(``%''). The remainder of the conversion specification includes, in
the following order,
· Zero or more of the following flags:
· a `#' character specifying that the value should be con‐
verted to an ``alternate form''. For c, d, i, n, p, s,
and u, conversions, this option has no effect. For o
conversions, the precision of the number is increased to
force the first character of the output string to a zero
(except if a zero value is printed with an explicit pre‐
cision of zero). For x and X conversions, a non-zero
result has the string 0x (or 0X for X conversions)
prepended to it. For e, E, f, g, and G, conversions, the
result will always contain a decimal point, even if no
digits follow it (normally, a decimal point appears in
the results of those conversions only if a digit fol‐
lows). For g and G conversions, trailing zeros are not
removed from the result as they would otherwise be.
· A zero ``0'' character specifying zero padding. For all
conversions except n, the converted value is padded on
the left with zeros rather than blanks. If a precision
is given with a numeric conversion ( d, i, o, u, i, x,
and X), the ``0'' flag is ignored.
· A minus sign (``-'') specifying left adjustment of the
converted value in the indicated field. Except for n
conversions, the converted value is padded on the right
with blanks, rather than on the left with blanks or
zeros. A ``-'' overrides a ``0'' if both are given.
· A space, specifying that a blank should be left before a
positive number produced by a signed conversion ( d, e,
E, f, g, G, or i).
· a `+' character specifying that a sign always be placed
before a number produced by a signed conversion. A ``+''
overrides a space if both are used.
· An optional digit string specifying a field width. If the con‐
verted value has fewer characters than the field width, it will
be padded on the left (or right, if the left-adjustment flag is
used) to make up the field width.
· An optional precision, in the form of a period (``.'') followed
by an optional digit string. If the digit string is omitted,
the precision is taken as zero. This gives the minimum number
of digits to appear for d, i, o, u, x, and X conversions, the
number of digits to appear after the decimal point for e, E, and
f conversions, the maximum number of significant digits for g
and G conversions, or the maximum number of characters to be
printed from a string for s conversions.
· The character h, specifying that a following d, i, o, u, x, or X
conversion corresponds to a short int or unsigned short int
argument, or that a following n conversion corresponds to a
pointer to a short int argument.
· the character l (ell) specifying that a following d, i, o, u, x,
or X conversion corresponds to a long int or unsigned long int
argument, or that a following n conversion corresponds to a
pointer to a long int argument.
· The character L specifying that a following e, E, f, g, or G
conversion corresponds to a long double argument (but note that
long double values are not currently supported by the VAX and
Tahoe compilers).
· A character which indicates the type of conversion to be
applied.
A field width or precision may be an asterisk (``*'') instead of a
digit string. In this case an int argument supplies the value. A neg‐
ative field width is treated as a left adjustment flag followed by a
positive field width; a negative precision is treated as though it were
missing.
The conversion characters and their meanings are:
diouxX The int (or appropriate variant) argument is converted to signed
decimal (d and i), unsigned octal (o), unsigned decimal (u), or
unsigned hexadecimal (x and X) notation respectively. The let‐
ters abcdef are used for x conversions; the letters ABCDEF are
used for X conversions. The precision, if any, gives the mini‐
mum number of digits that must appear; if the converted value
requires fewer digits, it is padded on the left with zeros.
DOU The long int argument is converted to signed decimal, unsigned
octal, or unsigned decimal, as if the format had been ld, lo, or
lu respectively. These conversion characters are deprecated,
and will eventually disappear.
eE The double argument is rounded and 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. If the precision is missing, 6 digits
are given; if the precision is explicitly zero, no decimal
point appears. An E conversion uses the letter E (rather than
e) to introduce the exponent. The exponent always contains at
least two digits; if the value is zero, the exponent is 00.
f The double argument is rounded and converted to decimal nota‐
tion in the style `[-]ddd.ddd' where the number of digits after
the decimal point is equal to the precision. If the precision
is missing, 6 digits are given; if the precision is explicitly
0, no digits and no decimal point are printed. If a decimal
point appears, at least one digit appears before it.
g The double argument is printed in style f or e (or E for G con‐
versions). The precision specifies the number of significant
digits. If the precision is missing, 6 digits are given; if
the precision is zero, it is treated as 1. Style e is used if
the exponent from its conversion is less than -4 or greater
than or equal to the precision. Trailing zeros are removed
from the fractional part of the result; a decimal point appears
only if it is followed by at least one digit.
c The int argument is converted to an unsigned char , and the
resulting character is printed.
s The char * argument is taken to be a string (character
pointer). Characters from the string are printed until a null
character is reached, or until the number of characters indi‐
cated by the precision have been printed, whichever occurs
first; if a precision is given, no null character need be
present.
p The void * pointer argument is printed in hexadecimal (as if by
``%x'' or ``%lx'').
n The number of characters written so far is stored into the
integer indicated by the int * (or variant) pointer argument.
No argument is converted.
% Prints 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 expanded to contain it. Similarly, padding takes place
only if the specified field width exceeds the actual width.
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, %02d:%.2d", weekday, month, day, hour, min);
To print pi to 5 decimals:
printf("pi = %.5f", 4*atan(1.0));
To allocate a 128 byte string and print into it:
#include <stdio.h>
#include <varargs.h>
char *newfmt(va_alist)
va_dcl
{
char *p, *malloc(), fmt;
va_list ap;
if ((p = malloc(128)) == NULL)
return (NULL);
va_start(ap);
fmt = va_arg(ap, char *);
(void) vsprintf(p, fmt, ap);
va_end(ap);
return (p);
}
SEE ALSOputc(3), scanf(3)BUGS
The conversion formats ``%D'', ``%O'', and ``%U'' are not standard and
are provided only for backward compatibility. The effect of padding
the ``%p'' format with zeros (either by the ``0'' flag or by specifying
a precision), and the benign effect (i.e., none) of the ``#'' flag on
``%n'' and ``%p'' conversions, as well as other nonsensical combina‐
tions such as ``%Ld'', are not standard; such combinations should be
avoided.
7th Edition October 22, 1987 PRINTF(3)