inet_lnaof(3)

1inet(3)                    Library Functions Manual                    inet(3)
2
3
4

NAME

6       inet_aton,    inet_addr,    inet_network,   inet_ntoa,   inet_makeaddr,
7       inet_lnaof, inet_netof - Internet address manipulation routines
8

LIBRARY

10       Standard C library (libc, -lc)
11

SYNOPSIS

13       #include <sys/socket.h>
14       #include <netinet/in.h>
15       #include <arpa/inet.h>
16
17       int inet_aton(const char *cp, struct in_addr *inp);
18
19       in_addr_t inet_addr(const char *cp);
20       in_addr_t inet_network(const char *cp);
21
22       [[deprecated]] char *inet_ntoa(struct in_addr in);
23
24       [[deprecated]] struct in_addr inet_makeaddr(in_addr_t net,
25                                                   in_addr_t host);
26
27       [[deprecated]] in_addr_t inet_lnaof(struct in_addr in);
28       [[deprecated]] in_addr_t inet_netof(struct in_addr in);
29
30   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
31
32       inet_aton(), inet_ntoa():
33           Since glibc 2.19:
34               _DEFAULT_SOURCE
35           In glibc up to and including 2.19:
36               _BSD_SOURCE || _BSD_SOURCE
37

DESCRIPTION

39       inet_aton() converts the Internet host address cp from  the  IPv4  num‐
40       bers-and-dots  notation  into  binary  form (in network byte order) and
41       stores it in the structure that inp  points  to.   inet_aton()  returns
42       nonzero  if the address is valid, zero if not.  The address supplied in
43       cp can have one of the following forms:
44
45       a.b.c.d   Each of the four numeric parts specifies a byte  of  the  ad‐
46                 dress;  the bytes are assigned in left-to-right order to pro‐
47                 duce the binary address.
48
49       a.b.c     Parts a and b specify the first two bytes of the  binary  ad‐
50                 dress.   Part c is interpreted as a 16-bit value that defines
51                 the rightmost two bytes of the binary address.  This notation
52                 is  suitable  for  specifying  (outmoded) Class B network ad‐
53                 dresses.
54
55       a.b       Part a specifies the first byte of the binary address.   Part
56                 b is interpreted as a 24-bit value that defines the rightmost
57                 three bytes of the binary address.  This notation is suitable
58                 for specifying (outmoded) Class A network addresses.
59
60       a         The  value  a is interpreted as a 32-bit value that is stored
61                 directly into the binary address without any byte  rearrange‐
62                 ment.
63
64       In  all  of  the  above  forms, components of the dotted address can be
65       specified in decimal, octal (with a leading 0), or hexadecimal, with  a
66       leading  0X).   Addresses in any of these forms are collectively termed
67       IPV4 numbers-and-dots notation.  The form that uses exactly four  deci‐
68       mal  numbers  is  referred to as IPv4 dotted-decimal notation (or some‐
69       times: IPv4 dotted-quad notation).
70
71       inet_aton() returns 1 if the supplied string  was  successfully  inter‐
72       preted, or 0 if the string is invalid (errno is not set on error).
73
74       The  inet_addr()  function  converts  the Internet host address cp from
75       IPv4 numbers-and-dots notation into binary data in network byte  order.
76       If  the input is invalid, INADDR_NONE (usually -1) is returned.  Use of
77       this  function  is  problematic  because  -1   is   a   valid   address
78       (255.255.255.255).    Avoid   its   use   in   favor   of  inet_aton(),
79       inet_pton(3), or getaddrinfo(3), which provide a cleaner way  to  indi‐
80       cate error return.
81
82       The  inet_network() function converts cp, a string in IPv4 numbers-and-
83       dots notation, into a number in host byte order suitable for use as  an
84       Internet  network  address.   On  success, the converted address is re‐
85       turned.  If the input is invalid, -1 is returned.
86
87       The inet_ntoa() function converts the Internet host address  in,  given
88       in  network  byte  order,  to a string in IPv4 dotted-decimal notation.
89       The string is returned in a statically allocated buffer,  which  subse‐
90       quent calls will overwrite.
91
92       The inet_lnaof() function returns the local network address part of the
93       Internet address in.  The returned value is in host byte order.
94
95       The inet_netof() function returns the network number part of the Inter‐
96       net address in.  The returned value is in host byte order.
97
98       The  inet_makeaddr()  function  is  the  converse  of  inet_netof() and
99       inet_lnaof().  It returns an Internet host address in network byte  or‐
100       der, created by combining the network number net with the local address
101       host, both in host byte order.
102
103       The  structure  in_addr  as  used  in   inet_ntoa(),   inet_makeaddr(),
104       inet_lnaof(), and inet_netof() is defined in <netinet/in.h> as:
105
106           typedef uint32_t in_addr_t;
107
108           struct in_addr {
109               in_addr_t s_addr;
110           };
111

ATTRIBUTES

113       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
114       tributes(7).
115
116       ┌─────────────────────────────────────┬───────────────┬────────────────┐
117       │Interface                            │ Attribute     │ Value          │
118       ├─────────────────────────────────────┼───────────────┼────────────────┤
119       │inet_aton(), inet_addr(),            │ Thread safety │ MT-Safe locale │
120       │inet_network(), inet_ntoa()          │               │                │
121       ├─────────────────────────────────────┼───────────────┼────────────────┤
122       │inet_makeaddr(), inet_lnaof(),       │ Thread safety │ MT-Safe        │
123       │inet_netof()                         │               │                │
124       └─────────────────────────────────────┴───────────────┴────────────────┘
125

STANDARDS

127       inet_addr()
128       inet_ntoa()
129              POSIX.1-2008.
130
131       inet_aton()
132              None.
133

STANDARDS

135       inet_addr()
136       inet_ntoa()
137              POSIX.1-2001, 4.3BSD.
138
139       inet_lnaof(), inet_netof(), and inet_makeaddr()  are  legacy  functions
140       that assume they are dealing with classful network addresses.  Classful
141       networking divides IPv4 network addresses into host and network  compo‐
142       nents at byte boundaries, as follows:
143
144       Class A   This  address  type  is  indicated by the value 0 in the most
145                 significant bit of the (network byte ordered)  address.   The
146                 network  address  is  contained in the most significant byte,
147                 and the host address occupies the remaining three bytes.
148
149       Class B   This address type is indicated by the binary value 10 in  the
150                 most  significant  two  bits of the address.  The network ad‐
151                 dress is contained in the two most significant bytes, and the
152                 host address occupies the remaining two bytes.
153
154       Class C   This address type is indicated by the binary value 110 in the
155                 most significant three bits of the address.  The network  ad‐
156                 dress  is  contained in the three most significant bytes, and
157                 the host address occupies the remaining byte.
158
159       Classful network addresses are now obsolete, having been superseded  by
160       Classless  Inter-Domain  Routing  (CIDR),  which divides addresses into
161       network and host components at arbitrary bit (rather than byte)  bound‐
162       aries.
163

NOTES

165       On  x86  architectures,  the  host byte order is Least Significant Byte
166       first (little endian), whereas the network byte order, as used  on  the
167       Internet, is Most Significant Byte first (big endian).
168

EXAMPLES

170       An  example  of  the use of inet_aton() and inet_ntoa() is shown below.
171       Here are some example runs:
172
173           $ ./a.out 226.000.000.037      # Last byte is in octal
174           226.0.0.31
175           $ ./a.out 0x7f.1               # First byte is in hex
176           127.0.0.1
177
178   Program source
179
180       #define _DEFAULT_SOURCE
181       #include <arpa/inet.h>
182       #include <stdio.h>
183       #include <stdlib.h>
184
185       int
186       main(int argc, char *argv[])
187       {
188           struct in_addr addr;
189
190           if (argc != 2) {
191               fprintf(stderr, "%s <dotted-address>\n", argv[0]);
192               exit(EXIT_FAILURE);
193           }
194
195           if (inet_aton(argv[1], &addr) == 0) {
196               fprintf(stderr, "Invalid address\n");
197               exit(EXIT_FAILURE);
198           }
199
200           printf("%s\n", inet_ntoa(addr));
201           exit(EXIT_SUCCESS);
202       }
203