1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
2 .\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
3 .\" <mtk.manpages@gmail.com>
5 .\" %%%LICENSE_START(VERBATIM)
6 .\" Permission is granted to make and distribute verbatim copies of this
7 .\" manual provided the copyright notice and this permission notice are
8 .\" preserved on all copies.
10 .\" Permission is granted to copy and distribute modified versions of this
11 .\" manual under the conditions for verbatim copying, provided that the
12 .\" entire resulting derived work is distributed under the terms of a
13 .\" permission notice identical to this one.
15 .\" Since the Linux kernel and libraries are constantly changing, this
16 .\" manual page may be incorrect or out-of-date. The author(s) assume no
17 .\" responsibility for errors or omissions, or for damages resulting from
18 .\" the use of the information contained herein. The author(s) may not
19 .\" have taken the same level of care in the production of this manual,
20 .\" which is licensed free of charge, as they might when working
23 .\" Formatted or processed versions of this manual, if unaccompanied by
24 .\" the source, must acknowledge the copyright and authors of this work.
27 .\" References consulted:
28 .\" Linux libc source code
29 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
31 .\" libc.info (from glibc distribution)
32 .\" Modified Sat Jul 24 19:12:00 1993 by Rik Faith <faith@cs.unc.edu>
33 .\" Modified Sun Sep 3 20:29:36 1995 by Jim Van Zandt <jrv@vanzandt.mv.com>
34 .\" Changed network into host byte order (for inet_network),
35 .\" Andreas Jaeger <aj@arthur.rhein-neckar.de>, 980130.
37 .\" Describe the various address forms supported by inet_aton().
38 .\" Clarify discussion of inet_lnaof(), inet_netof(), and inet_makeaddr().
39 .\" Add discussion of Classful Addressing, noting that it is obsolete.
40 .\" Added an EXAMPLE program.
42 .TH INET 3 2017-09-15 "GNU" "Linux Programmer's Manual"
44 inet_aton, inet_addr, inet_network, inet_ntoa, inet_makeaddr, inet_lnaof,
45 inet_netof \- Internet address manipulation routines
48 .B #include <sys/socket.h>
49 .B #include <netinet/in.h>
50 .B #include <arpa/inet.h>
52 .BI "int inet_aton(const char *" cp ", struct in_addr *" inp );
54 .BI "in_addr_t inet_addr(const char *" cp );
56 .BI "in_addr_t inet_network(const char *" cp );
58 .BI "char *inet_ntoa(struct in_addr " in );
60 .BI "struct in_addr inet_makeaddr(in_addr_t " net ", in_addr_t " host );
62 .BI "in_addr_t inet_lnaof(struct in_addr " in );
64 .BI "in_addr_t inet_netof(struct in_addr " in );
68 Feature Test Macro Requirements for glibc (see
69 .BR feature_test_macros (7)):
77 In glibc up to and including 2.19:
78 _BSD_SOURCE || _BSD_SOURCE
82 converts the Internet host address \fIcp\fP from the
83 IPv4 numbers-and-dots notation into binary form (in network byte order)
84 and stores it in the structure that \fIinp\fP points to.
86 returns nonzero if the address is valid, zero if not.
87 The address supplied in
89 can have one of the following forms:
92 Each of the four numeric parts specifies a byte of the address;
93 the bytes are assigned in left-to-right order to produce the binary address.
100 specify the first two bytes of the binary address.
103 is interpreted as a 16-bit value that defines the rightmost two bytes
104 of the binary address.
105 This notation is suitable for specifying (outmoded) Class B
111 specifies the first byte of the binary address.
114 is interpreted as a 24-bit value that defines the rightmost three bytes
115 of the binary address.
116 This notation is suitable for specifying (outmoded) Class A
122 is interpreted as a 32-bit value that is stored directly
123 into the binary address without any byte rearrangement.
125 In all of the above forms,
126 components of the dotted address can be specified in decimal,
127 octal (with a leading
129 or hexadecimal, with a leading
131 Addresses in any of these forms are collectively termed
132 .IR "IPV4 numbers-and-dots notation" .
133 The form that uses exactly four decimal numbers is referred to as
134 .IR "IPv4 dotted-decimal notation"
136 .IR "IPv4 dotted-quad notation" ).
139 returns 1 if the supplied string was successfully interpreted,
140 or 0 if the string is invalid
148 function converts the Internet host address
149 \fIcp\fP from IPv4 numbers-and-dots notation into binary data in network
151 If the input is invalid,
153 (usually \-1) is returned.
154 Use of this function is problematic because \-1 is a valid address
156 Avoid its use in favor of
161 which provide a cleaner way to indicate error return.
167 a string in IPv4 numbers-and-dots notation,
168 into a number in host byte order suitable for use as an
169 Internet network address.
170 On success, the converted address is returned.
171 If the input is invalid, \-1 is returned.
175 function converts the Internet host address
176 \fIin\fP, given in network byte order, to a string in IPv4
177 dotted-decimal notation.
178 The string is returned in a statically
179 allocated buffer, which subsequent calls will overwrite.
183 function returns the local network address part
184 of the Internet address \fIin\fP.
185 The returned value is in host byte order.
189 function returns the network number part of
190 the Internet address \fIin\fP.
191 The returned value is in host byte order.
195 function is the converse of
199 It returns an Internet host address in network byte order,
200 created by combining the network number \fInet\fP
201 with the local address \fIhost\fP, both in
204 The structure \fIin_addr\fP as used in
206 .BR inet_makeaddr (),
216 typedef uint32_t in_addr_t;
224 For an explanation of the terms used in this section, see
230 Interface Attribute Value
237 T} Thread safety MT-Safe locale
239 .BR inet_makeaddr (),
243 T} Thread safety MT-Safe
248 POSIX.1-2001, POSIX.1-2008, 4.3BSD.
251 is not specified in POSIX.1, but is available on most systems.
253 On x86 architectures, the host byte order is Least Significant Byte
254 first (little endian), whereas the network byte order, as used on the
255 Internet, is Most Significant Byte first (big endian).
261 are legacy functions that assume they are dealing with
262 .IR "classful network addresses" .
263 Classful networking divides IPv4 network addresses into host and network
264 components at byte boundaries, as follows:
267 This address type is indicated by the value 0 in the
268 most significant bit of the (network byte ordered) address.
269 The network address is contained in the most significant byte,
270 and the host address occupies the remaining three bytes.
273 This address type is indicated by the binary value 10 in the
274 most significant two bits of the address.
275 The network address is contained in the two most significant bytes,
276 and the host address occupies the remaining two bytes.
279 This address type is indicated by the binary value 110 in the
280 most significant three bits of the address.
281 The network address is contained in the three most significant bytes,
282 and the host address occupies the remaining byte.
284 Classful network addresses are now obsolete,
285 having been superseded by Classless Inter-Domain Routing (CIDR),
286 which divides addresses into network and host components at
287 arbitrary bit (rather than byte) boundaries.
289 An example of the use of
294 Here are some example runs:
298 .RB "$" " ./a.out 226.000.000.037" " # Last byte is in octal"
300 .RB "$" " ./a.out 0x7f.1 " " # First byte is in hex"
308 #include <arpa/inet.h>
313 main(int argc, char *argv[])
318 fprintf(stderr, "%s <dotted\-address>\\n", argv[0]);
322 if (inet_aton(argv[1], &addr) == 0) {
323 fprintf(stderr, "Invalid address\\n");
327 printf("%s\\n", inet_ntoa(addr));
334 .BR gethostbyname (3),
337 .BR inet_net_pton (3),