freebsd-skq/share/man/man9/printf.9

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.\" Copyright (c) 2004 Joerg Wunsch
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.Dd August 10, 2004
.Dt PRINTF 9
.Os
.Sh NAME
.Nm printf , uprintf , tprintf, log
.Nd formatted output conversion
.Sh SYNOPSIS
.In sys/types.h
.In sys/systm.h
.Ft int
.Fn printf "const char *fmt" ...
.Ft void
.Fn tprintf "struct proc *p" "int pri" "const char *fmt" ...
.Ft int
.Fn uprintf "const char *fmt" ...
.In sys/syslog.h
.Ft void
.Fn log "int pri" "const char *fmt" ...
.Sh DESCRIPTION
The
.Xr printf 9
family of functions are similar to the
.Xr printf 3
family of functions.
The different functions each use a different output stream.
The
.Fn uprintf
function outputs to the current process' controlling tty, while
.Fn printf
writes to the console as well as to the logging facility.
The
.Fn tprintf
function outputs to the tty associated with the process
.Fa p
and the logging facility if
.Fa pri
is not \-1.
The
.Fn log
function sends the message to the kernel logging facility, using
the log level as indicated by
.Fa pri .
.Pp
Each of these related functions use the
.Fa fmt
parameter in the same manner as
.Xr printf 3 .
However,
.Xr printf 9
adds two other conversion specifiers.
.Pp
The
.Cm \&%b
identifier expects two arguments: an
.Vt int
and a
.Vt "char *" .
These are used as a register value and a print mask for decoding bitmasks.
The print mask is made up of two parts: the base and the
arguments.
The base value is the output base expressed as an integer value;
for example, \e10 gives octal and \e20 gives hexadecimal.
The arguments are made up of a sequence of bit identifiers.
Each bit identifier begins with an integer value which is the number of the
bit this identifier describes.
The rest of the identifier is a string of characters containing the name of
the bit.
The string is terminated by either the bit number at the start of the next
bit identifier or
.Dv NUL
for the last bit identifier.
.Pp
The
.Cm \&%D
identifier is meant to assist in hexdumps.
It requires two arguments: a
.Vt "u_char *"
pointer and a
.Vt "char *"
string.
The memory pointed to be the pointer is output in hexadecimal one byte at
a time.
The string is used as a delimiter between individual bytes.
If present, a width directive will specify the number of bytes to display.
By default, 16 bytes of data are output.
.Pp
The
.Fn log
function uses
.Xr syslog 3
level values
.Dv LOG_DEBUG
through
.Dv LOG_EMERG
for its
.Fa pri
parameter (mistakenly called
.Sq priority
here).
Alternatively, if a
.Fa pri
of \-1 is given, the message will be appended to the last log message
started by a previous call to
.Fn log .
As these messages are generated by the kernel itself, the facility will
always be
.Dv LOG_KERN .
.Sh RETURN VALUES
The
.Fn printf
and the
.Fn uprintf
functions return the number of characters displayed.
.Sh EXAMPLES
This example demonstrates the use of the \&%b and \&%D conversion specifiers.
The function
.Bd -literal -offset indent
void
printf_test(void)
{

	printf("reg=%b\en", 3, "\e10\e2BITTWO\e1BITONE\en");
	printf("out: %4D\en", "AAAA", ":");
}
.Ed
.Pp
will produce the following output:
.Bd -literal -offset indent
reg=3<BITTWO,BITONE>
out: 41:41:41:41
.Ed
.Pp
The call
.Bd -literal -offset indent
log(LOG_DEBUG, "%s%d: been there.\en", sc->sc_name, sc->sc_unit);
.Ed
.Pp
will add the appropriate debug message at priority
.Dq Li kern.debug
to the system log.
.Sh SEE ALSO
.Xr printf 3 ,
.Xr syslog 3