.\"     $NetBSD: kprintf.9,v 1.9 2000/08/09 03:12:33 tv Exp $
.\"
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.\" by Jeremy Cooper.
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.Dd September 1, 1998
.Dt KPRINTF 9
.Os
.Sh NAME
.Nm printf, snprintf, vprintf, vsnprintf, uprintf, ttyprintf, tprintf
.Nd kernel formatted output conversion
.Sh SYNOPSIS
.Fd #include <sys/systm.h>
.Ft void
.Fn "printf" "const char *format" "..."
.Ft int
.Fn "snprintf" "char *buf" "size_t size" "const char *format" "..."
.Ft void
.Fn "vprintf" "const char *format" "va_list ap"
.Ft int
.Fn "vsnprintf" "char *buf" "size_t size" "const char *format" "va_list ap"
.Ft void
.Fn "uprintf" "const char *format" "..."
.Ft void
.Fn "ttyprintf" "struct tty *tty" "const char *format" "..."
.Fd #include <sys/tprintf.h>
.Ft tpr_t
.Fn "tprintf_open" "struct proc *p"
.Ft void
.Fn "tprintf" "tpr_t tpr" "const char *format" "..."
.Ft void
.Fn "tprintf_close" "tpr_t tpr"
.Sh DESCRIPTION
The
.Fn printf
family of functions allows the kernel to send formatted messages to various
output devices.
The functions
.Fn printf
and
.Fn vprintf
send formatted strings to the system console.
The functions
.Fn snprintf
and
.Fn vsnprintf
write output to a string buffer.  These four functions work similarly
to their user space counterparts, and are not described in detail here.
.Pp
The functions
.Fn uprintf
and
.Fn ttyprintf
send formatted strings to the current process's controlling tty and a specific
tty, respectively.
.Pp
The
.Fn tprintf
function sends formatted strings to a process's controlling tty,
via a handle of type tpr_t.
This allows multiple write operations to the tty with a guarantee that the
tty will be valid across calls.  A handle is acquired by calling
.Fn tprintf_open
with the target process as an argument.  This handle must be closed with
a matching call to
.Fn tprintf_close .
.Sh RETURN VALUES
The
.Fn snprintf
and
.Fn vsnprintf
functions return the number of characters placed in the buffer
.Fa buf .
.Sh SEE ALSO
.Xr printf 3 ,
.Xr printf 1 ,
.Xr bitmask_snprintf 9
.Sh CODE REFERENCES
.Pa sys/kern/subr_prf.c
.Sh HISTORY
The
.Fn sprintf
and
.Fn vsprintf
unsized string formatting functions are supported for compatibility only,
and are not documented here.  New code should use the size-limited
.Fn snprintf
and
.Fn vsnprintf
functions instead.
.Pp
In
.Nx 1.5
and earlier,
.Fn printf
supported more format strings than the user space
.Fn printf .
These nonstandard format strings are no longer supported.  For the
functionality provided by the former
.Li %b
format string, see
.Xr bitmask_snprintf 9 .
.Sh BUGS
The
.Fn uprintf
and
.Fn ttyprintf
functions should be used sparingly, if at all.  Where multiple lines of
output are required to reach a process's controlling terminal,
.Fn tprintf
is preferred.