1INET_PTON(3) Linux Programmer's Manual INET_PTON(3)
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6 inet_pton - convert IPv4 and IPv6 addresses from text to binary form
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9 #include <arpa/inet.h>
10 int inet_pton(int af, const char *restrict src, void *restrict dst);
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14 This function converts the character string src into a network address
15 structure in the af address family, then copies the network address
16 structure to dst. The af argument must be either AF_INET or AF_INET6.
17 dst is written in network byte order.
18 The following address families are currently supported:
20 AF_INET
22 src points to a character string containing an IPv4 network ad‐
23 dress in dotted-decimal format, "ddd.ddd.ddd.ddd", where ddd is
24 a decimal number of up to three digits in the range 0 to 255.
25 The address is converted to a struct in_addr and copied to dst,
26 which must be sizeof(struct in_addr)[24m (4) bytes (32 bits) long.
27 AF_INET6
29 src points to a character string containing an IPv6 network ad‐
30 dress. The address is converted to a struct in6_addr and copied
31 to dst, which must be sizeof(struct in6_addr) (16) bytes (128
32 bits) long. The allowed formats for IPv6 addresses follow these
33 rules:
34 1. The preferred format is x:x:x:x:x:x:x:x. This form consists
36 of eight hexadecimal numbers, each of which expresses a
37 16-bit value (i.e., each x can be up to 4 hex digits).
38 2. A series of contiguous zero values in the preferred format
40 can be abbreviated to ::. Only one instance of :: can occur
41 in an address. For example, the loopback address
42 0:0:0:0:0:0:0:1 can be abbreviated as ::1. The wildcard ad‐
43 dress, consisting of all zeros, can be written as ::.
44 3. An alternate format is useful for expressing IPv4-mapped IPv6
46 addresses. This form is written as x:x:x:x:x:x:d.d.d.d,
47 where the six leading xs are hexadecimal values that define
48 the six most-significant 16-bit pieces of the address (i.e.,
49 96 bits), and the ds express a value in dotted-decimal nota‐
50 tion that defines the least significant 32 bits of the ad‐
51 dress. An example of such an address is
52 ::FFFF:204.152.189.116.
53 See RFC 2373 for further details on the representation of IPv6
55 addresses.
56
58 inet_pton() returns 1 on success (network address was successfully con‐
59 verted). 0 is returned if src does not contain a character string rep‐
60 resenting a valid network address in the specified address family. If
61 af does not contain a valid address family, -1 is returned and errno is
62 set to EAFNOSUPPORT.
63
65 For an explanation of the terms used in this section, see at‐
66 tributes(7).
67 ┌─────────────────────────────────────┬───────────────┬────────────────┐
69 │Interface │ Attribute │ Value │
70 ├─────────────────────────────────────┼───────────────┼────────────────┤
71 │inet_pton() │ Thread safety │ MT-Safe locale │
72 └─────────────────────────────────────┴───────────────┴────────────────┘
73
75 POSIX.1-2001, POSIX.1-2008.
76
78 Unlike inet_aton(3) and inet_addr(3), inet_pton() supports IPv6 ad‐
79 dresses. On the other hand, inet_pton() accepts only IPv4 addresses in
80 dotted-decimal notation, whereas inet_aton(3) and inet_addr(3) allow
81 the more general numbers-and-dots notation (hexadecimal and octal num‐
82 ber formats, and formats that don't require all four bytes to be ex‐
83 plicitly written). For an interface that handles both IPv6 addresses,
84 and IPv4 addresses in numbers-and-dots notation, see getaddrinfo(3).
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87 AF_INET6 does not recognize IPv4 addresses. An explicit IPv4-mapped
88 IPv6 address must be supplied in src instead.
89
91 The program below demonstrates the use of inet_pton() and inet_ntop(3).
92 Here are some example runs:
93 $ ./a.out i6 0:0:0:0:0:0:0:0
95 ::
96 $ ./a.out i6 1:0:0:0:0:0:0:8
97 1::8
98 $ ./a.out i6 0:0:0:0:0:FFFF:204.152.189.116
99 ::ffff:204.152.189.116
100 Program source
102 #include <arpa/inet.h>
104 #include <stdio.h>
105 #include <stdlib.h>
106 #include <string.h>
107 int
109 main(int argc, char *argv[])
110 {
111 unsigned char buf[sizeof(struct in6_addr)];
112 int domain, s;
113 char str[INET6_ADDRSTRLEN];
114 if (argc != 3) {
116 fprintf(stderr, "Usage: %s {i4|i6|<num>} string\n", argv[0]);
117 exit(EXIT_FAILURE);
118 }
119 domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :
121 (strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);
122 s = inet_pton(domain, argv[2], buf);
124 if (s <= 0) {
125 if (s == 0)
126 fprintf(stderr, "Not in presentation format");
127 else
128 perror("inet_pton");
129 exit(EXIT_FAILURE);
130 }
131 if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {
133 perror("inet_ntop");
134 exit(EXIT_FAILURE);
135 }
136 printf("%s\n", str);
138 exit(EXIT_SUCCESS);
140 }
141
143 getaddrinfo(3), inet(3), inet_ntop(3)
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146 This page is part of release 5.12 of the Linux man-pages project. A
147 description of the project, information about reporting bugs, and the
148 latest version of this page, can be found at
149 https://www.kernel.org/doc/man-pages/.
150Linux 2021-03-22 INET_PTON(3)