fprintf, printf, sprintf, vfprintf, vprintf, vsprintf - print formatted output
int fprintf(FILE *f, char *format, ...);
int printf(char *format, ...);
int sprintf(char *s, char *format, ...);
int vfprintf(FILE *f, char *format, char *args);
int vprintf(char *format, char *args);
int vsprintf(char *s, char *format, char *args);
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 charac-
ter (\0) in consecutive bytes starting at s; it is the user's responsibility to ensure
that enough storage is available. Vfprintf, vprintf, and vsprintf are the same, except
the args argument is a pointer to an argument in an argument list of the calling function,
and the effect is as if the calling function's argument list from that point on is passed
to the printf routines.
Each function returns the number of characters transmitted (not including the \0 in the
case of sprintf), or a negative value if an output error was encountered.
These functions convert, format, and print their trailing arguments under control of a
format string. The format contains two types of objects: plain characters, which are sim-
ply 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 arguments 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 follow-
ing 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 con-
verted value has fewer characters than the field width, it will be padded with spa-
ces 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 pro-
moted 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 following d, i, o, u, x, or X conversion character applies
to a long or unsigned long argument; an optional l specifying that a following 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 argu-
ments specifying field width or precision, 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
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 conver-
sion 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 decimal point appears in the result of
these conversions only if a digit follows it). For g and G conversions, trail-
ing 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 pad-
ding 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 behavior 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), unsigned octal (o),
unsigned decimal (u), or unsigned hexadecimal notation (x or X); 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 is expanded with leading zeros.
The default precision is 1. The result of converting a zero value with a preci-
sion 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 decimal 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 exponent always contains at least
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
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 preci-
sion 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
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 charac-
ter type using %s conversion, or a pointer cast to be a pointer to void using %P conver-
sion), 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
fopen(2), fscanf(2), print(2)
There is no way to print a wide character (rune); use print(2) or bio(2).