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1 | .\" Hey Emacs! This file is -*- nroff -*- source. |
2 | .\" | |
3 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) | |
054f5228 | 4 | .\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk <mtk.manpages@gmail.com> |
fea681da MK |
5 | .\" |
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. | |
9 | .\" | |
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. | |
c13182ef | 14 | .\" |
fea681da MK |
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16 | .\" manual page may be incorrect or out-of-date.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 | |
21 | .\" professionally. | |
c13182ef | 22 | .\" |
fea681da MK |
23 | .\" Formatted or processed versions of this manual, if unaccompanied by |
24 | .\" the source, must acknowledge the copyright and authors of this work. | |
25 | .\" | |
26 | .\" References consulted: | |
27 | .\" Linux libc source code | |
28 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
29 | .\" 386BSD man pages | |
30 | .\" libc.info (from glibc distribution) | |
31 | .\" Modified Sat Jul 24 19:12:00 1993 by Rik Faith <faith@cs.unc.edu> | |
32 | .\" Modified Sun Sep 3 20:29:36 1995 by Jim Van Zandt <jrv@vanzandt.mv.com> | |
33 | .\" Changed network into host byte order (for inet_network), | |
34 | .\" Andreas Jaeger <aj@arthur.rhein-neckar.de>, 980130. | |
054f5228 MK |
35 | .\" 2008-06-19, mtk |
36 | .\" Describe the various address forms supported by inet_aton(). | |
37 | .\" Clarify discussion of inet_lnaof(), inet_netof(), and inet_makeaddr(). | |
38 | .\" Add discussion of Classful Addressing, noting that it is obsolete. | |
39 | .\" Added an EXAMPLE program. | |
fea681da | 40 | .\" |
054f5228 | 41 | .TH INET 3 2008-06-19 "GNU" "Linux Programmer's Manual" |
fea681da | 42 | .SH NAME |
c13182ef | 43 | inet_aton, inet_addr, inet_network, inet_ntoa, inet_makeaddr, inet_lnaof, |
fea681da MK |
44 | inet_netof \- Internet address manipulation routines |
45 | .SH SYNOPSIS | |
46 | .nf | |
47 | .B #include <sys/socket.h> | |
48 | .B #include <netinet/in.h> | |
49 | .B #include <arpa/inet.h> | |
50 | .sp | |
51 | .BI "int inet_aton(const char *" cp ", struct in_addr *" inp ); | |
52 | .sp | |
53 | .BI "in_addr_t inet_addr(const char *" cp ); | |
54 | .sp | |
55 | .BI "in_addr_t inet_network(const char *" cp ); | |
56 | .sp | |
57 | .BI "char *inet_ntoa(struct in_addr " in ); | |
58 | .sp | |
59 | .BI "struct in_addr inet_makeaddr(int " net ", int " host ); | |
60 | .sp | |
61 | .BI "in_addr_t inet_lnaof(struct in_addr " in ); | |
62 | .sp | |
63 | .BI "in_addr_t inet_netof(struct in_addr " in ); | |
64 | .fi | |
cc4615cc MK |
65 | .sp |
66 | .in -4n | |
67 | Feature Test Macro Requirements for glibc (see | |
68 | .BR feature_test_macros (7)): | |
69 | .in | |
70 | .sp | |
71 | .BR inet_aton (), | |
72 | .BR inet_ntoa (): | |
73 | _BSD_SOURCE || _SVID_SOURCE | |
fea681da | 74 | .SH DESCRIPTION |
60a90ecd MK |
75 | .BR inet_aton () |
76 | converts the Internet host address \fIcp\fP from the | |
054f5228 MK |
77 | IPv4 numbers-and-dots notation into binary form (in network byte order) |
78 | and stores it in the structure that \fIinp\fP points to. | |
60a90ecd | 79 | .BR inet_aton () |
054f5228 MK |
80 | returns non-zero if the address is valid, zero if not. |
81 | The address supplied in | |
82 | .I cp | |
83 | can have one of the following forms: | |
84 | .TP 10 | |
85 | .I a.b.c.d | |
86 | Each of the for numeric parts specifies a byte of the address; | |
87 | the bytes are assigned in left-to-right order to produce the binary address. | |
88 | .TP | |
89 | .I a.b.c | |
90 | Parts | |
91 | .I a | |
92 | and | |
93 | .I b | |
94 | specify the first two bytes of the binary address. | |
95 | Part | |
96 | .I c | |
97 | is interpreted as a 16-bit value that defines the rightmost two bytes | |
98 | of the binary address. | |
99 | This notation is suitable for specifying (outmoded) Class B | |
100 | network addresses. | |
101 | .TP | |
102 | .I a.b | |
103 | Part | |
104 | .I a | |
105 | specifies the first byte of the binary address. | |
106 | Part | |
107 | .I b | |
108 | is interpreted as a 24-bit value that defines the rightmost three bytes | |
109 | of the binary address. | |
110 | This notation is suitable for specifying (outmoded) Class C | |
111 | network addresses. | |
112 | .TP | |
113 | .I a | |
114 | The value | |
115 | .I a | |
116 | is interpreted as a 32-bit value that is stored directly | |
117 | into the binary address without any byte rearrangement. | |
118 | .PP | |
119 | In all of the above forms, | |
120 | components of the dotted address can be specified in decimal, | |
121 | octal (with a leading | |
122 | .IR 0 ), | |
123 | or hexadecimal, with a leading | |
124 | .IR 0X ). | |
125 | Addresses in any of these forms are collectively termed | |
126 | .IR "IPV4 numbers-and-dots notation" . | |
127 | The form that uses exactly four decimal numbers is referred to as | |
128 | .IR "IPv4 dotted-decimal notation" | |
129 | (or sometimes: | |
130 | .IR "IPv4 dotted-quad notation" ). | |
fea681da | 131 | .PP |
60a90ecd MK |
132 | The |
133 | .BR inet_addr () | |
134 | function converts the Internet host address | |
054f5228 | 135 | \fIcp\fP from IPv4 numbers-and-dots notation into binary data in network |
c13182ef | 136 | byte order. |
2f0af33b MK |
137 | If the input is invalid, |
138 | .B INADDR_NONE | |
139 | (usually \-1) is returned. | |
054f5228 MK |
140 | Use of this function is problematic because \-1 is a valid address |
141 | (255.255.255.255). | |
142 | Avoid its use in favor of | |
60a90ecd | 143 | .BR inet_aton (), |
054f5228 MK |
144 | .BR inet_pton (3), |
145 | or | |
146 | .BR getaddrinfo (3) | |
147 | which provide a cleaner way to indicate error return. | |
fea681da | 148 | .PP |
60a90ecd MK |
149 | The |
150 | .BR inet_network () | |
054f5228 MK |
151 | function converts |
152 | .IR cp , | |
153 | a string in IPv4 numbers-and-dots notation, | |
154 | into a number in host byte order suitable for use as an | |
155 | Internet network address. | |
156 | On success, the converted address is returned. | |
7cc028fb | 157 | If the input is invalid, \-1 is returned. |
fea681da | 158 | .PP |
60a90ecd MK |
159 | The |
160 | .BR inet_ntoa () | |
161 | function converts the Internet host address | |
054f5228 MK |
162 | \fIin\fP, given in network byte order, to a string in IPv4 |
163 | dotted-decimal notation. | |
c13182ef | 164 | The string is returned in a statically |
fea681da MK |
165 | allocated buffer, which subsequent calls will overwrite. |
166 | .PP | |
60a90ecd | 167 | The |
60a90ecd | 168 | .BR inet_lnaof () |
054f5228 | 169 | function returns the local network address part |
c13182ef | 170 | of the Internet address \fIin\fP. |
054f5228 | 171 | The returned value is in host byte order. |
fea681da | 172 | .PP |
60a90ecd MK |
173 | The |
174 | .BR inet_netof () | |
175 | function returns the network number part of | |
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176 | the Internet address \fIin\fP. |
177 | The returned value is in host byte order. | |
178 | .PP | |
179 | The | |
180 | .BR inet_makeaddr () | |
181 | function is the converse of | |
61792fc6 | 182 | .BR inet_netof () |
054f5228 MK |
183 | and |
184 | .BR inet_lnaof (). | |
185 | It returns an Internet host address in network byte order, | |
186 | created by combining the network number \fInet\fP | |
187 | with the local address \fIhost\fP, both in | |
188 | host byte order. | |
fea681da | 189 | .PP |
60a90ecd MK |
190 | The structure \fIin_addr\fP as used in |
191 | .BR inet_ntoa (), | |
192 | .BR inet_makeaddr (), | |
3c775eb7 | 193 | .BR inet_lnaof () |
60a90ecd MK |
194 | and |
195 | .BR inet_netof () | |
a9a13a50 MK |
196 | is defined in |
197 | .I <netinet/in.h> | |
198 | as: | |
fea681da | 199 | .sp |
bd191423 | 200 | .in +4n |
fea681da | 201 | .nf |
9f8162f9 MK |
202 | typedef uint32_t in_addr_t; |
203 | ||
fea681da | 204 | struct in_addr { |
9f8162f9 MK |
205 | in_addr_t s_addr; |
206 | }; | |
fea681da | 207 | .fi |
bd191423 | 208 | .in |
2b2581ee MK |
209 | .SH "CONFORMING TO" |
210 | 4.3BSD. | |
054f5228 | 211 | .BR inet_addr () |
2b2581ee MK |
212 | and |
213 | .BR inet_ntoa () | |
214 | are specified in POSIX.1-2001. | |
054f5228 MK |
215 | .BR inet_aton () |
216 | is not specified in POSIX.1.-2001, but is available on most systems. | |
19c98696 | 217 | .SH NOTES |
054f5228 MK |
218 | On the i386 the host byte order is Least Significant Byte |
219 | first (little endian), whereas the network byte order, as used on the | |
220 | Internet, is Most Significant Byte first (big endian). | |
221 | ||
222 | .BR inet_lnaof (), | |
223 | .BR inet_netof (), | |
224 | and | |
225 | .BR inet_makeaddr () | |
226 | are legacy functions that assume they are dealing with | |
227 | .IR "classful network addresses" . | |
228 | Classful networking divides IPv4 network addresses into host and network | |
229 | components at byte boundaries, as follows: | |
230 | .TP 10 | |
231 | Class A | |
232 | This address type is indicated by the value 0 in the | |
233 | most significant bit of the (network byte ordered) address. | |
234 | The network address is contained in the most significant byte, | |
235 | and the host address occupies the remaining three bytes. | |
236 | .TP | |
237 | Class B | |
238 | This address type is indicated by the binary value 10 in the | |
239 | most significant two bits of the address. | |
240 | The network address is contained in the two most significant bytes, | |
241 | and the host address occupies the remaining two bytes. | |
242 | .TP | |
243 | Class C | |
244 | This address type is indicated by the binary value 110 in the | |
245 | most significant three bits of the address. | |
246 | The network address is contained in the three most significant bytes, | |
247 | and the host address occupies the remaining byte. | |
248 | .PP | |
249 | Classful network addresses are now obolete, | |
250 | having been superseded by Classless Inter-Domain Routing (CIDR), | |
251 | which divides addresses into network and host components at | |
252 | arbitrary bit (rather than byte) boundaries. | |
253 | .SH EXAMPLE | |
254 | An example of the use of | |
255 | .BR inet_aton () | |
256 | and | |
257 | .BR inet_ntoa () | |
258 | is shown below. | |
259 | Here are some example runs: | |
260 | .in +4n | |
261 | .nf | |
262 | ||
263 | $ ./a.out 226.000.000.037 # Last byte is in octal | |
264 | 226.0.0.31 | |
265 | $ ./a.out 0x7f.1 # First byte is in hex | |
266 | 127.0.0.1 | |
267 | ||
268 | .fi | |
269 | .in | |
270 | .nf | |
271 | #define _BSD_SOURCE | |
272 | #include <arpa/inet.h> | |
273 | #include <stdio.h> | |
274 | #include <stdlib.h> | |
275 | ||
276 | int | |
277 | main(int argc, char *argv[]) | |
278 | { | |
279 | struct in_addr addr; | |
280 | ||
281 | if (argc != 2) { | |
282 | fprintf(stderr, "%s <dotted\-address>\\n", argv[0]); | |
283 | exit(EXIT_FAILURE); | |
284 | } | |
285 | ||
286 | if (inet_aton(argv[1], &addr) == 0) { | |
287 | perror("inet_aton"); | |
288 | exit(EXIT_FAILURE); | |
289 | } | |
290 | ||
291 | printf("%s\\n", inet_ntoa(addr)); | |
292 | exit(EXIT_SUCCESS); | |
293 | } | |
294 | .fi | |
fea681da | 295 | .SH "SEE ALSO" |
054f5228 MK |
296 | .BR byteorder (3), |
297 | .BR getaddrinfo (3), | |
fea681da | 298 | .BR gethostbyname (3), |
054f5228 | 299 | .BR getnameinfo (3), |
fea681da MK |
300 | .BR getnetent (3), |
301 | .BR inet_ntop (3), | |
302 | .BR inet_pton (3), | |
303 | .BR hosts (5), | |
304 | .BR networks (5) |