.\"	$OpenBSD: inet_net_ntop.3,v 1.4 2022/09/11 06:38:10 jmc Exp $
.\"	$NetBSD: inet_net.3,v 1.1 1997/06/18 02:25:27 lukem Exp $
.\"
.\" Copyright (c) 1997 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Luke Mewburn.
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.Dd $Mdocdate: September 11 2022 $
.Dt INET_NET_NTOP 3
.Os
.Sh NAME
.Nm inet_net_ntop ,
.Nm inet_net_pton
.Nd Internet network number manipulation routines
.Sh SYNOPSIS
.In sys/socket.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
.Vt 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
.Dv 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
.Vt 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
Caution:
The
.Fa dst
field should be zeroed before calling
.Fn inet_net_pton
as the function will only fill the number of bytes necessary to
encode the network number in network byte order.
.Pp
The only values for
.Fa af
currently supported 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)
The external representation of Internet network numbers may be specified in
one of the following forms:
.Bd -literal -offset indent
a
a.b
a.b.c
a.b.c.d
.Ed
.Pp
Any of the above four forms may have
.Dq Li /bits
appended where
.Dq Li bits
is in the range
.Li 0-32
and is used to explicitly specify the number of bits in the network address.
When
.Dq Li /bits
is not specified, the number of bits in the network address is calculated
as the larger of the number of bits in the class to which the address
belongs and the number of bits provided rounded up modulo 8.
Examples:
.Pp
.Bl -tag -width 10.1.2.3/24 -offset indent -compact
.It Li 10
an 8-bit network number (class A), value
.Li 10.0.0.0 .
.It Li 192
a 24-bit network number (class C), value
.Li 192.0.0.0 .
.It Li 10.10
a 16-bit network number, value
.Li 10.10.0.0 .
.It Li 10.1.2
a 24-bit network number, value
.Li 10.1.2.0 .
.It Li 10.1.2.3
a 32-bit network number, value
.Li 10.1.2.3 .
.It Li 10.1.2.3/24
a 24-bit network number (explicit), value
.Li 10.1.2.3 .
.El
.Pp
Note that when the number of bits is specified using
.Dq Li /bits
notation, the value of the address still includes all bits supplied
in the external representation, even those bits which are the host
part of an Internet address.
Also, unlike
.Xr inet_pton 3
where the external representation is assumed to be a host address, the
external representation for
.Fn inet_net_pton
is assumed to be a network address.
Thus
.Dq Li 10.1
is assumed to be
.Dq Li 10.1.0.0
not
.Dq Li 10.0.0.1
.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)
See
.Xr inet_pton 3
for valid external representations of IP version 6 addresses.
A valid external representation may have
.Dq Li /bits
appended where
.Dq Li bits
is in the range
.Li 0-128
and is used to explicitly specify the number of bits in the network address.
When
.Dq Li /bits
is not specified, 128 is used.
Note that when the number of bits is specified using
.Dq Li /bits
notation, the value of the address still includes all bits supplied
in the external representation, even those bits which are the host
part of an Internet address.
.Sh SEE ALSO
.Xr htonl 3 ,
.Xr inet_pton 3 ,
.Xr inet 4 ,
.Xr hosts 5
.Sh HISTORY
The
.Nm inet_net_ntop
and
.Nm inet_net_pton
functions first appeared in BIND 4.9.4.