2.11BSD/src/man/man3/printf.3

.\"	@(#)printf.3s	6.5.1 (2.11BSD) 1995/04/02
.\"
.TH PRINTF 3S "August 10, 1988"
.AT 3
.SH NAME
printf, fprintf, sprintf, vfprintf, vsprintf \- formatted output conversion
.SH SYNOPSIS
.B #include <stdio.h>
.PP
.B char *printf(format
.RB [ ,
arg ] ...
.B )
.br
.B char *format;
.PP
.B char *fprintf(stream, format
.RB [ ,
arg ] ...
.B )
.br
.SM
.B FILE
.B *stream;
.br
.B char *format;
.PP
.B int sprintf(s, format
.RB [ ,
arg ] ...
.B )
.br
.B char *s, *format;
.PP
.B #include <varargs.h>
.br
.B char *vprintf(format, args)
.br
.B char *format;
.br
.B va_list args;
.PP
.B char *vfprintf(stream, format, args)
.br
.B FILE *stream;
.br
.B char *format;
.br
.B va_list args;
.PP
.B int vsprintf(s, format, args)
.br
.B char *s, *format;
.br
.B va_list args;
.SH DESCRIPTION
.I Printf
places output on the standard output stream
.BR stdout .
.I Fprintf
places output on the named output
.IR stream .
.I Sprintf
places `output' in the string
.IR s ,
followed by the character `\\0'.
Alternate forms, in which the arguments have already been
captured using the variable-length argument facilities of
.IR varargs (3),
are available under the names
.IR vprintf ,
.IR vfprintf ,
and
.IR vsprintf .
.PP
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
.I arg
.IR printf .
.PP
Each conversion specification is introduced by the character
.BR % .
The remainder of the conversion specification includes
in the following order
.TP
.B \(bu
a minus sign `\-' which specifies
.I "left adjustment"
of the converted value in the indicated field;
.TP
.B \(bu
an optional digit string specifying a
.I "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;
if the field width begins with a zero,
zero-padding will be done instead of blank-padding;
.TP
.B \(bu
an optional period, followed by
an optional digit string giving a
.I 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;
.TP
.B \(bu
the character
.B l
specifying that a following
.BR d ,
.BR o ,
.BR x ,
or
.B u
corresponds to a long integer
.IR arg ;
.TP
.B \(bu
a character which indicates the type of
conversion to be applied.
.PP
A field width or precision may be `*' instead of a digit string.
In this case an integer
.I arg
supplies
the field width or precision.
.PP
The conversion characters
and their meanings are
.TP
.B dox
The integer
.I arg
is converted to signed decimal, unsigned octal, or
unsigned hexadecimal notation respectively.
.TP
.B f
The float or double
.I arg
is converted to decimal notation
in the style `[\fB\-\fR]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.
.TP
.B e
The float or double
.I arg
is converted in the style
`[\fB\-\fR]d\fB.\fRddd\fBe\fR\(+-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.
.TP
.B g
The float or double
.I arg
is printed in style
.BR d ,
in style
.BR f ,
or in
style
.BR e ,
whichever gives full precision in minimum space.
.TP
.B c
The character
.I arg
is printed.
.TP
.B s
.I Arg
is taken to be a string (character pointer)
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.
.TP
.B u
The unsigned integer
.I arg
is converted to decimal
and printed (the result will be in the
range 0 through MAXUINT, where MAXUINT equals 4294967295 on a VAX-11
and 65535 on a PDP-11).
.TP
.B %
Print a `%'; no argument is converted.
.PP
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
.I printf
are printed as by 
.IR putc (3S).
.PP
.SH "RETURN VALUE"
The functions all return
the number of characters printed, or -1 if an error occurred.
.SH EXAMPLES
.br
To print a date and time in the form `Sunday, July 3, 10:02',
where
.I weekday
and
.I month
are pointers to null-terminated strings:
.RS
.HP
.nh
printf("%s, %s %d, %02d:%02d", weekday, month, day, hour, min);
.RE
.hy
.PP
To print
.if n pi
.if t \(*p
to 5 decimals:
.IP
printf("pi = %.5f", 4*atan(1.0));
.SH "SEE ALSO"
putc(3S), scanf(3S)
.SH BUGS
Very wide fields (>300 characters) fail.
.LP
Only \fIsprintf\fP and \fIvsprintf\fP return a count of characters 
transferred.
.LP
The functions still supports \fI%D\fP, \fI%O\fP, \fI%U\fP and 
\fI%X\fP.  Do not
use these formats, as they will be disappearing real soon now.