1inet_pton(3) Library Functions 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 Standard C library (libc, -lc)
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12 #include <arpa/inet.h>
13 int inet_pton(int af, const char *restrict src, void *restrict dst);
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17 This function converts the character string src into a network address
18 structure in the af address family, then copies the network address
19 structure to dst. The af argument must be either AF_INET or AF_INET6.
20 dst is written in network byte order.
21 The following address families are currently supported:
23 AF_INET
25 src points to a character string containing an IPv4 network ad‐
26 dress in dotted-decimal format, "ddd.ddd.ddd.ddd", where ddd is
27 a decimal number of up to three digits in the range 0 to 255.
28 The address is converted to a struct in_addr and copied to dst,
29 which must be sizeof(struct in_addr)[24m (4) bytes (32 bits) long.
30 AF_INET6
32 src points to a character string containing an IPv6 network ad‐
33 dress. The address is converted to a struct in6_addr and copied
34 to dst, which must be sizeof(struct in6_addr) (16) bytes (128
35 bits) long. The allowed formats for IPv6 addresses follow these
36 rules:
37 • The preferred format is x:x:x:x:x:x:x:x. This form consists
39 of eight hexadecimal numbers, each of which expresses a
40 16-bit value (i.e., each x can be up to 4 hex digits).
41 • A series of contiguous zero values in the preferred format
43 can be abbreviated to ::. Only one instance of :: can occur
44 in an address. For example, the loopback address
45 0:0:0:0:0:0:0:1 can be abbreviated as ::1. The wildcard ad‐
46 dress, consisting of all zeros, can be written as ::.
47 • An alternate format is useful for expressing IPv4-mapped IPv6
49 addresses. This form is written as x:x:x:x:x:x:d.d.d.d,
50 where the six leading xs are hexadecimal values that define
51 the six most-significant 16-bit pieces of the address (i.e.,
52 96 bits), and the ds express a value in dotted-decimal nota‐
53 tion that defines the least significant 32 bits of the ad‐
54 dress. An example of such an address is
55 ::FFFF:204.152.189.116.
56 See RFC 2373 for further details on the representation of IPv6
58 addresses.
59
61 inet_pton() returns 1 on success (network address was successfully con‐
62 verted). 0 is returned if src does not contain a character string rep‐
63 resenting a valid network address in the specified address family. If
64 af does not contain a valid address family, -1 is returned and errno is
65 set to EAFNOSUPPORT.
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68 For an explanation of the terms used in this section, see at‐
69 tributes(7).
70 ┌─────────────────────────────────────┬───────────────┬────────────────┐
72 │Interface │ Attribute │ Value │
73 ├─────────────────────────────────────┼───────────────┼────────────────┤
74 │inet_pton() │ Thread safety │ MT-Safe locale │
75 └─────────────────────────────────────┴───────────────┴────────────────┘
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78 Unlike inet_aton(3) and inet_addr(3), inet_pton() supports IPv6
79 addresses. On the other hand, inet_pton() accepts only IPv4 addresses
80 in dotted-decimal notation, whereas inet_aton(3) and inet_addr(3) allow
81 the more general numbers-and-dots notation (hexadecimal and octal
82 number formats, and formats that don't require all four bytes to be
83 explicitly written). For an interface that handles both IPv6
84 addresses, and IPv4 addresses in numbers-and-dots notation, see
85 getaddrinfo(3).
86
88 POSIX.1-2008.
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91 POSIX.1-2001.
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94 AF_INET6 does not recognize IPv4 addresses. An explicit IPv4-mapped
95 IPv6 address must be supplied in src instead.
96
98 The program below demonstrates the use of inet_pton() and inet_ntop(3).
99 Here are some example runs:
100 $ ./a.out i6 0:0:0:0:0:0:0:0
102 ::
103 $ ./a.out i6 1:0:0:0:0:0:0:8
104 1::8
105 $ ./a.out i6 0:0:0:0:0:FFFF:204.152.189.116
106 ::ffff:204.152.189.116
107 Program source
109 #include <arpa/inet.h>
111 #include <stdio.h>
112 #include <stdlib.h>
113 #include <string.h>
114 int
116 main(int argc, char *argv[])
117 {
118 unsigned char buf[sizeof(struct in6_addr)];
119 int domain, s;
120 char str[INET6_ADDRSTRLEN];
121 if (argc != 3) {
123 fprintf(stderr, "Usage: %s {i4|i6|<num>} string\n", argv[0]);
124 exit(EXIT_FAILURE);
125 }
126 domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :
128 (strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);
129 s = inet_pton(domain, argv[2], buf);
131 if (s <= 0) {
132 if (s == 0)
133 fprintf(stderr, "Not in presentation format");
134 else
135 perror("inet_pton");
136 exit(EXIT_FAILURE);
137 }
138 if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {
140 perror("inet_ntop");
141 exit(EXIT_FAILURE);
142 }
143 printf("%s\n", str);
145 exit(EXIT_SUCCESS);
147 }
148
150 getaddrinfo(3), inet(3), inet_ntop(3)
151Linux man-pages 6.05 2023-07-20 inet_pton(3)