term% cat index.txt FPRINTF(2) System Calls Manual FPRINTF(2)
NAME
fprintf, printf, sprintf, snprintf, vfprintf, vprintf, vsprintf, vs‐
nprintf - print formatted output
SYNOPSIS
#include <u.h>
#include <stdio.h>
int fprintf(FILE *f, char *format, ...)
int printf(char *format, ...)
int sprintf(char *s, char *format, ...)
int snprintf(char *s, int n, char *format, ...)
int vfprintf(FILE *f, char *format, va_list args)
int vprintf(char *format, va_list args)
int vsprintf(char *s, char *format, va_list args)
int vsnprintf(char *s, int n, char *format, va_list args)
DESCRIPTION
Fprintf places output on the named output stream f (see fopen(2)).
Printf places output on the standard output stream stdout. 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. Snprintf is like sprintf but writes at most n
bytes (including the null character) into s. Vfprintf, vprintf, vs‐
nprintf, and vsprintf are the same, except the args argument is the ar‐
gument list of the calling function, and the effect is as if the call‐
ing function's argument list from that point on is passed to the printf
routines.
Each function returns the number of characters transmitted (not includ‐
ing the \0 in the case of sprintf and friends), or a negative value if
an output error was encountered.
These functions convert, format, and print their trailing arguments un‐
der control of a format string. The format contains two types of ob‐
jects: plain characters, which are simply copied to the output stream,
and conversion specifications, each of which results in fetching of
zero or more arguments. The results are undefined if there are argu‐
ments of the wrong type or too few arguments for the format. If the
format is exhausted while arguments remain, the excess are ignored.
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 with spaces on the left (or
right, if the left adjustment, described later, has been given)
to the field width.
An optional precision that gives the minimum number of digits to
appear for the d, i, o, u, x, and 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 conversions, or the maximum number of characters to be
written from a string in s conversion. The precision takes the
form of a period (.) followed by an optional decimal integer;
if the integer is omitted, it is treated as zero.
An optional h specifying that a following d, i, o, u, x or X
conversion specifier applies to a short int or unsigned short
argument (the argument will have been promoted according to the
integral promotions, and its value shall be converted to short
or unsigned short before printing); an optional h specifying
that a following n conversion specifier applies to a pointer to
a short argument; an optional l (ell) specifying that a follow‐
ing d, i, o, u, x, or X conversion character applies to a long
or unsigned long argument; an optional l specifying that a fol‐
lowing n conversion specifier applies to a pointer to a long int
argument; or an optional L specifying that a following e, E, f,
g, or G conversion specifier applies to a long double argument.
If an h, l, or L appears with any other conversion specifier,
the behavior is undefined.
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 int arg supplies the
field width or precision. The arguments specifying field width or pre‐
cision, or both, shall appear (in that order) before the argument (if
any) to be converted. A negative field width argument is taken as a -
flag followed by a positive field width. A negative precision is taken
as if it were missing.
The flag characters and their meanings are:
- The result of the conversion is left-justified within the
field.
+ The result of a signed conversion always begins with a sign
(+ or -).
blank If the first character of a signed conversion is not a sign,
or a signed conversion results in no characters, a blank is
prefixed to the result. This implies that if the blank and +
flags both appear, the blank flag is ignored.
# The result is to be converted to an ‘‘alternate form.'' 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 has 0x or 0X prefixed to it. For e, E, f, g,
and G conversions, the result always contains a decimal
point, even if no digits follow the point (normally, a deci‐
mal point appears in the result of these conversions only if
a digit follows it). For g and G conversions, trailing zeros
are not be removed from the result as they normally are. For
other conversions, the behavior is undefined.
0 For d, i, o, u, x, X, e, E, f, g, and G conversions, leading
zeros (following any indication of sign or base) are used to
pad the field width; no space padding is performed. If the 0
and - flags both appear, the 0 flag will be ignored. For d,
i, o, u, x, and X conversions, if a precision is specified,
the 0 flag will be ignored. For other conversions, the be‐
havior is undefined.
The conversion characters and their meanings are:
d,o,u,x,X The integer arg is converted to signed decimal (d or i), un‐
signed octal (o), unsigned decimal (u), or unsigned hexadeci‐
mal notation (x or X); the letters abcdef are used for x con‐
version and the letters ABCDEF for X conversion. The preci‐
sion specifies the minimum number of digits to appear; if the
value being converted can be represented in fewer digits, it
is expanded with leading zeros. The default precision is 1.
The result of converting a zero value with a precision of
zero is no characters.
f The double argument is converted to decimal notation in the
style [-]ddd.ddd, where the number of digits after the deci‐
mal point is equal to the precision specification. If the
precision is missing, it is taken as 6; if the precision is
explicitly no decimal point appears.
e,E The double argument is converted in the style [-]d.ddde±dd,
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, it is taken as 6; if the precision is
zero, no decimal point appears. The E format code produces a
number with E instead of e introducing the exponent. The ex‐
ponent always contains at least two digits.
g,G The double argument is printed in style f or e (or in style E
in the case of a G conversion specifier), with the precision
specifying the number of significant digits. If an explicit
precision is zero, it is taken as 1. The style used depends
on the value converted: style e is used only if the exponent
resulting from the conversion is less than -4 or greater than
or equal to the precision. Trailing zeros are removed from
the fractional portion of the result; a decimal point appears
only if it is followed by a digit.
c The int argument is converted to an unsigned char, and the
resulting character is written.
s The argument is taken to be a string (character pointer) and
characters from the string are printed until a null character
(\0) is encountered or 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 zero value for the
argument yields undefined results.
P The void* argument is printed in an implementation-defined
way (for Plan 9: the address as hexadecimal number).
n The argument shall be a pointer to an integer into which is
written the number of characters written to the output stream
so far by this call to fprintf. No argument is converted.
% Print a %; no argument is converted.
If a conversion specification is invalid, the behavior is undefined.
If any argument is, or points to, a union or an aggregate (except for
an array of character type using %s conversion, or a pointer cast to be
a pointer to void using %P conversion), the behavior is undefined.
In no case does a nonexistent 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 the conversion result.
SOURCE
/sys/src/libstdio
SEE ALSO
fopen(2), fscanf(2), print(2)
BUGS
There is no way to print a wide character (rune); use print(2) or
bio(2).
FPRINTF(2)