intro.1, _exit.2, access.2, alarm.2, alloc_hugepages.2, arch_prctl.2, bind.2, chdir...

[thirdparty/man-pages.git] / man3 / inet.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(verbatim)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\"     libc.info (from glibc distribution)
.\" Modified Sat Jul 24 19:12:00 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Sun Sep  3 20:29:36 1995 by Jim Van Zandt <jrv@vanzandt.mv.com>
.\" Changed network into host byte order (for inet_network),
.\"     Andreas Jaeger <aj@arthur.rhein-neckar.de>, 980130.
.\" 2008-06-19, mtk
.\"     Describe the various address forms supported by inet_aton().
.\"     Clarify discussion of inet_lnaof(), inet_netof(), and inet_makeaddr().
.\"     Add discussion of Classful Addressing, noting that it is obsolete.
.\"     Added an EXAMPLE program.
.\"
.TH INET 3  2013-02-10 "GNU" "Linux Programmer's Manual"
.SH NAME
inet_aton, inet_addr, inet_network, inet_ntoa, inet_makeaddr, inet_lnaof,
inet_netof \- Internet address manipulation routines
.SH SYNOPSIS
.nf
.B #include <sys/socket.h>
.B #include <netinet/in.h>
.B #include <arpa/inet.h>
.sp
.BI "int inet_aton(const char *" cp ", struct in_addr *" inp );
.sp
.BI "in_addr_t inet_addr(const char *" cp );
.sp
.BI "in_addr_t inet_network(const char *" cp );
.sp
.BI "char *inet_ntoa(struct in_addr " in );
.sp
.BI "struct in_addr inet_makeaddr(int " net ", int " host );
.sp
.BI "in_addr_t inet_lnaof(struct in_addr " in );
.sp
.BI "in_addr_t inet_netof(struct in_addr " in );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR inet_aton (),
.BR inet_ntoa ():
_BSD_SOURCE || _SVID_SOURCE
.SH DESCRIPTION
.BR inet_aton ()
converts the Internet host address \fIcp\fP from the
IPv4 numbers-and-dots notation into binary form (in network byte order)
and stores it in the structure that \fIinp\fP points to.
.BR inet_aton ()
returns nonzero if the address is valid, zero if not.
The address supplied in
.I cp
can have one of the following forms:
.TP 10
.I a.b.c.d
Each of the four numeric parts specifies a byte of the address;
the bytes are assigned in left-to-right order to produce the binary address.
.TP
.I a.b.c
Parts
.I a
and
.I b
specify the first two bytes of the binary address.
Part
.I c
is interpreted as a 16-bit value that defines the rightmost two bytes
of the binary address.
This notation is suitable for specifying (outmoded) Class B
network addresses.
.TP
.I a.b
Part
.I a
specifies the first byte of the binary address.
Part
.I b
is interpreted as a 24-bit value that defines the rightmost three bytes
of the binary address.
This notation is suitable for specifying (outmoded) Class C
network addresses.
.TP
.I a
The value
.I a
is interpreted as a 32-bit value that is stored directly
into the binary address without any byte rearrangement.
.PP
In all of the above forms,
components of the dotted address can be specified in decimal,
octal (with a leading
.IR 0 ),
or hexadecimal, with a leading
.IR 0X ).
Addresses in any of these forms are collectively termed
.IR "IPV4 numbers-and-dots notation" .
The form that uses exactly four decimal numbers is referred to as
.IR "IPv4 dotted-decimal notation"
(or sometimes:
.IR "IPv4 dotted-quad notation" ).
.PP
The
.BR inet_addr ()
function converts the Internet host address
\fIcp\fP from IPv4 numbers-and-dots notation into binary data in network
byte order.
If the input is invalid,
.B INADDR_NONE
(usually \-1) is returned.
Use of this function is problematic because \-1 is a valid address
(255.255.255.255).
Avoid its use in favor of
.BR inet_aton (),
.BR inet_pton (3),
or
.BR getaddrinfo (3)
which provide a cleaner way to indicate error return.
.PP
The
.BR inet_network ()
function converts
.IR cp ,
a string in IPv4 numbers-and-dots notation,
into a number in host byte order suitable for use as an
Internet network address.
On success, the converted address is returned.
If the input is invalid, \-1 is returned.
.PP
The
.BR inet_ntoa ()
function converts the Internet host address
\fIin\fP, given in network byte order, to a string in IPv4
dotted-decimal notation.
The string is returned in a statically
allocated buffer, which subsequent calls will overwrite.
.PP
The
.BR inet_lnaof ()
function returns the local network address part
of the Internet address \fIin\fP.
The returned value is in host byte order.
.PP
The
.BR inet_netof ()
function returns the network number part of
the Internet address \fIin\fP.
The returned value is in host byte order.
.PP
The
.BR inet_makeaddr ()
function is the converse of
.BR inet_netof ()
and
.BR inet_lnaof ().
It returns an Internet host address in network byte order,
created by combining the network number \fInet\fP
with the local address \fIhost\fP, both in
host byte order.
.PP
The structure \fIin_addr\fP as used in
.BR inet_ntoa (),
.BR inet_makeaddr (),
.BR inet_lnaof ()
and
.BR inet_netof ()
is defined in
.I <netinet/in.h>
as:
.sp
.in +4n
.nf
typedef uint32_t in_addr_t;

struct in_addr {
    in_addr_t s_addr;
};
.fi
.in
.SH CONFORMING TO
4.3BSD.
.BR inet_addr ()
and
.BR inet_ntoa ()
are specified in POSIX.1-2001.
.BR inet_aton ()