printf, fprintf, sprintf - formatted output conversion
int printf(format [ , arg... ] )
int fprintf(stream, format [ , arg... ] )
char *sprintf(s, format [ , arg... ] )
char *s, *format;
SYSTEM V SYNOPSIS
The routines above are available as shown, except:
int sprintf(s, format [ , arg... ] )
char *s, *format;
The following are provided for XPG2 compatibility:
#define nl_printf printf
#define nl_fprintf fprintf
#define nl_sprintf sprintf
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
Each of these functions converts, formats, and prints its args under
control of the format. The format 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 con-
version and printing 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 either the % character
or by the character sequence %digit$, after which the following appear
o Zero or more flags, which modify the meaning of the conver-
o 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. The padding is with blanks unless the field
width digit string starts with a zero, in which case the pad-
ding is with zeros.
o 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 conver-
sions, the maximum number of significant digits for the g and
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. Padding specified
by the precision overrides the padding specified by the field
o 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 character is ignored.
o A character that indicates the type of conversion to be
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 conversion 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 fol-
lowed by a positive field width. If the precision argument is nega-
tive, it will be changed to zero.
The flag characters and their meanings are:
- The result of the conversion will be left-justified within
+ 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 prefixed to the result. This implies that if
the blank and + flags both appear, the blank flag will be
# This flag specifies that the value is to be converted to an
"alternate form". For c, d, i, s, and u conversions, the
flag has no effect. For o conversion, it increases the pre-
cision 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 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 be removed from
the result (which they normally are).
The conversion characters and their meanings are:
The integer arg is converted to signed decimal (d or i),
unsigned octal (o), unsigned decimal (u), or unsigned hexa-
decimal notation (x, p, and X), respectively; the letters
abcdef are used for x and p 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 rep-
resented in fewer digits, it will be expanded with leading
zeroes. For compatibility with older versions, padding with
leading zeroes may alternatively be specified by prepending a
zero to the field width. This does not imply an octal value
for the field width. The default precision is 1. The result
of converting a zero value with a precision of zero is a null
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, 6 digits are given; if the preci-
sion is explicitly 0, no digits and no decimal point are
e,E The float or double arg is converted in the style
"[-]d.ddde+-ddd," where there is one digit before the decimal
point and the number of digits after it is equal to the pre-
cision; 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 intro-
ducing the exponent. The exponent always contains at least
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 or 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.
The e, E, f, g, and G formats print IEEE indeterminate values (infinity
or not-a-number) as "Infinity" or "NaN" respectively.
c The character arg is printed.
s The arg is taken to be a string (character pointer) and char-
acters from the string are printed until a null character
(\0) is encountered or until the number of characters indi-
cated by the precision specification is reached. If the pre-
cision is missing, it is taken to be infinite, so all charac-
ters up to the first null character are printed. A NULL
value for arg will yield undefined results.
n The argument arg is a pointer to an integer into which is
written the number of characters written to the output so far
by this call to one of the printf() functions. No argument
% Print 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 simply expanded to contain the conversion result. Padding
takes place only if the specified field width exceeds the actual width.
Characters generated by printf() and fprintf() are printed as if
putc(3S) had been called.
All forms of the printf() functions allow for the insertion of a lan-
guage dependent radix character in the output string. The radix char-
acter is defined by the program's locale (category LC_NUMERIC). In the
"C" locale, or in a locale where the radix character is not defined,
the radix character defaults to `.'.
Conversions can be applied to the nth argument in the argument list,
rather than the next unused argument. In this case, the conversion
character % is replaced by the sequence %digit$, where digit is a deci-
mal integer n in the range [1,9], giving the position of the argument
in the argument list. This feature provides for the definition of for-
mat strings that select arguments in an order appropriate to specific
In format strings containing the %digit$ form of a conversion specifi-
cation, a field width or precision may be indicated by the sequence
*digit$, where digit is a decimal integer in the range [1,9] giving the
position in the argument list of an integer arg containing the field
width or precision.
The format string can contain either numbered argument specifications
(that is, %digit$ and *digit$), or unnumbered argument specifications
(that is % and *), but not both. The results of mixing numbered and
unnumbered specifications is undefined. When numbered argument speci-
fications are used, specifying the nth argument requires that all the
leading arguments, from the first to the (n-1)th be specified in the
SYSTEM V DESCRIPTION
XPG2 requires that nl_printf, nl_fprintf and nl_sprintf be defined as
printf, fprintf and sprintf, respectively for backward compatibility
On success, printf() and fprintf() return the number of characters
transmitted, excluding the null character. On failure, they return
sprintf() returns s.
SYSTEM V RETURN VALUES
On success, sprintf() returns the number of characters transmitted,
excluding the null character. On failure, it returns EOF.
printf(format, weekday, month, day, hour, min);
In American usage, format could be a pointer to the string:
"%s, %s %d, %d:%.2d\n"
producing the message:
Sunday, July 3,10:02
Whereas for German usage, format could be a pointer to the string:
producing the message:
To print pi to 5 decimal places:
printf("pi = %.5f", 4 * atan(1. 0));
econvert(3), putc(3S), scanf(3V), setlocale(3V), varargs(3),
Very wide fields (>128 characters) fail.
21 January 1990 PRINTF(3V)