printf(3S) UNIX System V(BSD Compatibility Package) printf(3S)
NAME
printf, fprintf, sprintf, vprintf, vfprintf, vsprintf - formatted output
conversion
SYNOPSIS
cc [ flag. . . ] file . . . -lucb
#include <stdio.h>
int printf(format [ , arg ] ... )
char *format;
int fprintf(stream, format [ , arg ] ... )
FILE *stream;
char *format;
char *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;
char *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 responsibility to ensure that enough storage is
available.
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).
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
conversion 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.
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printf(3S) UNIX System V(BSD Compatibility Package) printf(3S)
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 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 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 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 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 character 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 conversion letter is seen, so the args specifying field
width or precision must appear before the arg (if any) to be converted.
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 -).
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.
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printf(3S) UNIX System V(BSD Compatibility Package) printf(3S)
# 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 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 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:
d,i,o,u,x,X
The integer arg is converted to signed decimal (d or i), unsigned
octal (o), unsigned decimal (u), or unsigned hexadecimal notation
(x and 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. (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 string.
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 precision is explicitly 0,
no digits and no decimal point are printed.
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 precision; 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 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 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.
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printf(3S) UNIX System V(BSD Compatibility Package) printf(3S)
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 until the number of characters 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 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.
RETURN VALUE
Upon success, printf and fprintf return the number of characters
transmitted, excluding the null character. vprintf and vfprintf return
the number of characters transmitted. sprintf and vsprintf always return
s. If an output error is encountered, printf, fprint, vprintf, and
vfprintf, return EOF.
EXAMPLE
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);
To print pi to 5 decimal places:
printf("pi = %.5f", 4 * atan(1. 0));
SEE ALSO
econvert(3)
putc(3S), scanf(3S), varargs(5), vprintf(3S) in the Programmer's
Reference Manual
NOTES
Very wide fields (>128 characters) fail.
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