printf
, fprintf
, sprintf
---format output#include <stdio.h> int printf(const char *format [, arg, ...]); int fprintf(FILE *fd, const char *format [, arg, ...]); int sprintf(char *str, const char *format [, arg, ...]);Description
printf
accepts a series of arguments, applies to each a
format specifier from *format
, and writes the
formatted data to stdout
, terminated with a null character.
The behavior of printf
is undefined if there are not enough
arguments for the format.
printf
returns when it reaches the end of the format string.
If there are more arguments than the format requires, excess
arguments are ignored.
fprintf
and sprintf
are identical to printf
, other than the
destination of the formatted output: fprintf
sends the
output to a specified file fd, while sprintf
stores the
output in the specified char array str. For sprintf
,
the behavior is also undefined if the output *str
overlaps with one of the arguments.
format is a pointer to a charater string containing two types of
objects: ordinary characters (other than %
), which are
copied unchanged to the output, and conversion
specifications, each of which is introduced by %
.
(To include %
in the output, use %%
in the format string.)
A conversion specification has the following form:
%[flags][width][.prec][size][type]
The fields of the conversion specification have the following meanings:
-
), plus (+
),
space ( ), zero (0
), and sharp (#
). They can
appear in any combination.
-
+
" " (space)
+
) flag both appear,
the space flag is ignored.
0
d
, i
, o
, u
,
x
, X
, e
, E
, f
, g
, or G
: leading zeroes,
are used to pad the field width (following any indication of sign or
base); no spaces are used for padding. If the zero (0
) and
minus (-
) flags both appear, the zero (0
) flag will
be ignored. For d
, i
, o
, u
, x
, and X
conversions, if a precision prec is specified, the zero (0
)
flag is ignored.
Note that 0
is interpreted as a flag, not as the beginning
of a field width.
#
0
x
0x
prefix.
X
0X
prefix.
e, E or f
g or G
e
or E
, but trailing zeroes
are not removed.
all others
*
), in which case an int
argument is used as the field width. Negative field widths
are not supported; if you attempt to specify a negative field
width, it is interpreted as a minus (-
) flag followed by a
positive field width.
.
'
(a period). This field gives the maximum number of
characters to print in a conversion; the minimum number of
digits of an integer to print, for conversions with type
d
, i
, o
, u
, x
, and X
; the maximum number of
significant digits, for the g
and G
conversions;
or the number of digits to print after the decimal
point, for e
, E
, and f
conversions. You can specify
the precision either directly as a decimal integer or
indirectly by using an asterisk (*
), in which case
an int
argument is used as the precision. Supplying a negative
precision is equivalent to omitting the precision.
If only a period is specified the precision is zero.
If a precision appears with any other conversion type
than those listed here, the behavior is undefined.
h
, l
, and L
are optional size characters which
override the default way that printf
interprets the
data type of the corresponding argument. h
forces
the following d
, i
, o
, u
, x
or X
conversion
type to apply to a short
or unsigned short
. h
also
forces a following n
type to apply to
a pointer to a short
. Similarily, an
l
forces the following d
, i
, o
, u
,
x
or X
conversion type to apply to a long
or
unsigned long
. l
also forces a following n
type to
apply to a pointer to a long
. If an h
or an l
appears with another conversion
specifier, the behavior is undefined. L
forces a
following e
, E
, f
, g
or G
conversion type to
apply to a long double
argument. If L
appears with
any other conversion type, the behavior is undefined.
printf
performs.
Here is a table of these:
%
%
)
c
s
d
int
(same as i
)
i
int
(same as d
)
o
int
u
int
x
abcdef
as
digits beyond 9
); takes an int
X
ABCDEF
as
digits beyond 9
); takes an int
f
[-]9999.9999
; takes
a floating point number
e
[-]9.9999e[+|-]999
; takes a
floating point number
E
e
, but using E
to introduce the
exponent; takes a floating point number
g
f
or e
form, based on given
value and precision--trailing zeros and the decimal point are
printed only if necessary; takes a floating point number
G
g
, but using E
for the exponent if an
exponent is needed; takes a floating point number
n
int
p
unsigned long
(same as Lu
).
Returns
sprintf
returns the number of bytes in the output string,
save that the concluding NULL
is not counted.
printf
and fprintf
return the number of characters transmitted.
If an error occurs, printf
and fprintf
return EOF
. No
error returns occur for sprintf
.
Portability
The ANSI C standard specifies that implementations must
support at least formatted output of up to 509 characters.
Supporting OS subroutines required: close
, fstat
, isatty
,
lseek
, read
, sbrk
, write
.