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 *src, void *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 └────────────┴───────────────┴────────────────┘
74 POSIX.1-2001, POSIX.1-2008.
75
77 Unlike inet_aton(3) and inet_addr(3), inet_pton() supports IPv6 ad‐
78 dresses. On the other hand, inet_pton() accepts only IPv4 addresses in
79 dotted-decimal notation, whereas inet_aton(3) and inet_addr(3) allow
80 the more general numbers-and-dots notation (hexadecimal and octal num‐
81 ber formats, and formats that don't require all four bytes to be ex‐
82 plicitly written). For an interface that handles both IPv6 addresses,
83 and IPv4 addresses in numbers-and-dots notation, see getaddrinfo(3).
84
86 AF_INET6 does not recognize IPv4 addresses. An explicit IPv4-mapped
87 IPv6 address must be supplied in src instead.
88
90 The program below demonstrates the use of inet_pton() and inet_ntop(3).
91 Here are some example runs:
92 $ ./a.out i6 0:0:0:0:0:0:0:0
94 ::
95 $ ./a.out i6 1:0:0:0:0:0:0:8
96 1::8
97 $ ./a.out i6 0:0:0:0:0:FFFF:204.152.189.116
98 ::ffff:204.152.189.116
99 Program source
101 #include <arpa/inet.h>
103 #include <stdio.h>
104 #include <stdlib.h>
105 #include <string.h>
106 int
108 main(int argc, char *argv[])
109 {
110 unsigned char buf[sizeof(struct in6_addr)];
111 int domain, s;
112 char str[INET6_ADDRSTRLEN];
113 if (argc != 3) {
115 fprintf(stderr, "Usage: %s {i4|i6|<num>} string\n", argv[0]);
116 exit(EXIT_FAILURE);
117 }
118 domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :
120 (strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);
121 s = inet_pton(domain, argv[2], buf);
123 if (s <= 0) {
124 if (s == 0)
125 fprintf(stderr, "Not in presentation format");
126 else
127 perror("inet_pton");
128 exit(EXIT_FAILURE);
129 }
130 if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {
132 perror("inet_ntop");
133 exit(EXIT_FAILURE);
134 }
135 printf("%s\n", str);
137 exit(EXIT_SUCCESS);
139 }
140
142 getaddrinfo(3), inet(3), inet_ntop(3)
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145 This page is part of release 5.10 of the Linux man-pages project. A
146 description of the project, information about reporting bugs, and the
147 latest version of this page, can be found at
148 https://www.kernel.org/doc/man-pages/.
149Linux 2020-06-09 INET_PTON(3)