NAME
printf, fprintf, sprintf - formatted output conversion

SYNOPSIS
#include <stdio.h>

int printf(format [, arg ] ... )
const char *format;

fprintf(stream, format [, arg ] ... )
FILE *stream;
const char *format;

sprintf(s, format [, arg ] ... )
char *s;
const char *format;

snprintf(s, n, format [, arg ] ... )
char *s;
size_t n;
const char *format;

#include <varargs.h>
vprintf(format, args)
const char *format;
va_list args;

vfprintf(stream, format, args)
FILE *stream;
const char *format;
va_list args;

vsprintf(s, format, args)
char *s;
const char *format;
va_list args;

vsnprintf(s, n, format, args)
char *s;
size_t n;
char *format;
va_list args;

DESCRIPTION
Printf places output on the standard output stream stdout. Fprintf
places output on the named output stream. Sprintf and snprintf
place ‘output’ in the string s, followed by the character ‘ ’.
Snprintf places at most n characters in the string, including the
‘ ’. Alternate forms, in which the arguments have already been
captured using the variable-length argument facilities of
varargs(3), are available under the names vprintf, vfprintf,
vsprintf, and vsnprintf.

Each of these functions converts, formats, and prints its arguments
after the first under control of the first argument. The first
argument 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 the next successive arg printf.

Each conversion specification is introduced by the 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
converted 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.
For x(X) conversion, a non-zero result has the string
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 only appears in the results of those
conversions if a digit follows the decimal point). For g
and G conversions, trailing zeros are not removed from
the result as they would otherwise be;

a minus sign ‘-’ which specifies left adjustment of the
converted value in the indicated field;

a ‘+’ character specifying that there should always be a
sign placed before the number when using signed
conversions;

a space specifying that a blank should be left before a
positive number during a signed conversion. A ‘+’
overrides a space if both are used;

a zero ‘0’ character indicating that zero-padding should
be used rather than blank-padding. A ‘-’ overrides a ‘0’
if both are used;

an optional digit string specifying a field width; if the
converted value has fewer characters than the field width it
will be blank-padded on the left (or right, if the left-
adjustment indicator has been given) to make up the field
width (note that a leading zero is a flag, but an embedded
zero is part of a field width);

an optional period, followed by an optional digit string
giving a precision which specifies the number of digits to
appear after the decimal point, for e- and f-conversion, or
the maximum number of characters to be printed from a string;
if the digit string is missing, the precision is treated as
zero;

the character l (ell) specifying that a following d, i, o, u,
x, or X corresponds to a long integer arg, or that a following
n corresponds to a pointer to a long integer arg;

the character h specifying that a following d, i, o, u, x, or
X corresponds to a short integer arg, or that a following n
corresponds to a pointer to a short integer arg;

a character which indicates the type of conversion to be
applied.

A field width or precision may be ‘*’ instead of a digit string.
In this case an integer arg supplies the field width or precision.

The conversion characters and their meanings are

diouxX
The integer arg is converted to signed decimal (d and i),
unsigned octal (o), unsigned decimal (u), or unsigned
hexadecimal (x and X); the letters abcdef are used for x
conversion and the letters ABCDEF are used for X.

eE The double arg is 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 specification for the
argument; when the precision is missing, 6 digits are
produced. An uppercase E is used for ‘E’ conversion.

f The double arg is converted to decimal notation in the style
‘[-]ddd.ddd’ where the number of d’s after the decimal point
is equal to the precision specification for the argument. If
the precision is missing, 6 digits are given; if the precision
is explicitly 0, no digits and no decimal point are printed.

gG The double arg is printed in style f or in style e (E)
whichever gives full precision in minimum space.

c The int arg is converted to an unsigned char, and the
resulting character is printed.

s Arg is taken to be a string (char *) and characters from the
string are printed until a null character or until the number
of characters indicated by the precision specification is
reached; however if the precision is 0 or missing all
characters up to a null are printed.

p Arg is taken to be a pointer to void; it is printed in style
x.

n Arg is taken to be a pointer to an integer (int *) through
which is stored the number of characters written to the output
stream (or string) so far by this call to printf (or fprintf,
etc.).

% Print a ‘%’; no argument is converted.

In no case does a non-existent or small field width cause
truncation of a field; padding takes place only if the specified
field width exceeds the actual width. Characters generated by
printf are printed as by putc(3).

RETURN VALUE
The functions all return the number of characters printed, or -1 if
an error occurred.

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:%02d", weekday, month, day, hour,
min);

To print pi to 5 decimals:

printf("pi = %.5f", 4*atan(1.0));