.\"	$NetBSD: inet_net.3,v 1.2.8.2 2008/04/30 13:10:51 martin Exp $
.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Luke Mewburn.
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.Dd December 8, 2001
.Dt INET_NET 3
.Os
.Sh NAME
.Nm inet_net_ntop ,
.Nm inet_net_pton
.Nd Internet network number manipulation routines
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/socket.h
.In netinet/in.h
.In arpa/inet.h
.Ft char *
.Fn inet_net_ntop "int af" "const void *src" "int bits" "char *dst" "size_t size"
.Ft int
.Fn inet_net_pton "int af" "const char *src" "void *dst" "size_t size"
.Sh DESCRIPTION
The
.Fn inet_net_ntop
function converts an Internet network number from network format (usually a
.Ft struct in_addr
or some other binary form, in network byte order) to CIDR presentation format
(suitable for external display purposes).
.Fa bits
is the number of bits in
.Fa src
that are the network number.
It returns NULL if a system error occurs (in which case,
.Va errno
will have been set), or it returns a pointer to the destination string.
.Pp
The
.Fn inet_net_pton
function converts a presentation format Internet network number (that is,
printable form as held in a character string) to network format (usually a
.Ft struct in_addr
or some other internal binary representation, in network byte order).
It returns the number of bits (either computed based on the class, or
specified with /CIDR), or -1 if a failure occurred
(in which case
.Va errno
will have been set.
It will be set to
.Er ENOENT
if the Internet network number was not valid).
.Pp
The currently supported values for
.Fa af
are
.Dv AF_INET
and
.Dv AF_INET6 .
.Fa size
is the size of the result buffer
.Fa dst .
.Sh NETWORK NUMBERS (IP VERSION 4)
Internet network numbers may be specified in one of the following forms:
.Bd -literal -offset indent
a.b.c.d/bits
a.b.c.d
a.b.c
a.b
a
.Ed
.Pp
When four parts are specified, each is interpreted
as a byte of data and assigned, from left to right,
to the four bytes of an Internet network number.  Note
that when an Internet network number is viewed as a 32-bit
integer quantity on a system that uses little-endian
byte order (such as the
.Tn Intel 386, 486
and
.Tn Pentium
processors) the bytes referred to above appear as
.Dq Li d.c.b.a .
That is, little-endian bytes are ordered from right to left.
.Pp
When a three part number is specified, the last
part is interpreted as a 16-bit quantity and placed
in the right-most two bytes of the Internet network number.
This makes the three part number format convenient
for specifying Class B network numbers as
.Dq Li 128.net.host .
.Pp
When a two part number is supplied, the last part
is interpreted as a 24-bit quantity and placed in
the right most three bytes of the Internet network number.
This makes the two part number format convenient
for specifying Class A network numbers as
.Dq Li net.host .
.Pp
When only one part is given, the value is stored
directly in the Internet network number without any byte
rearrangement.
.Pp
All numbers supplied as
.Dq parts
in a
.Ql  \&.
notation
may be decimal, octal, or hexadecimal, as specified
in the C language (i.e., a leading 0x or 0X implies
hexadecimal; otherwise, a leading 0 implies octal;
otherwise, the number is interpreted as decimal).
.\"
.\" .Sh NETWORK NUMBERS (IP VERSION 6)
.\" XXX - document this!
.\"
.Sh SEE ALSO
.Xr byteorder 3 ,
.Xr inet 3 ,
.Xr networks 5
.Sh HISTORY
The
.Nm inet_net_ntop
and
.Nm inet_net_pton
functions appeared in BIND 4.9.4 and thence
.Nx 1.3 .
Support for
.Dv AF_INET6
appeared in
.Nx 1.6 .