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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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inet_pton(3) Library Functions Manual inet_pton(3)
inet_pton - convert IPv4 and IPv6 addresses from text to binary
form
Standard C library (libc, -lc)
#include <arpa/inet.h>
int inet_pton(int af, const char *restrict src, void *restrict dst);
This function converts the character string src into a network
address structure in the af address family, then copies the
network address structure to dst. The af argument must be either
AF_INET or AF_INET6. dst is written in network byte order.
The following address families are currently supported:
AF_INET
src points to a character string containing an IPv4 network
address in dotted-decimal format, "ddd.ddd.ddd.ddd", where
ddd is a decimal number of up to three digits in the range
0 to 255. The address is converted to a struct in_addr and
copied to dst, which must be sizeof(struct in_addr) (4)
bytes (32 bits) long.
AF_INET6
src points to a character string containing an IPv6 network
address. The address is converted to a struct in6_addr and
copied to dst, which must be sizeof(struct in6_addr) (16)
bytes (128 bits) long. The allowed formats for IPv6
addresses follow these rules:
• The preferred format is x:x:x:x:x:x:x:x. This form
consists of eight hexadecimal numbers, each of which
expresses a 16-bit value (i.e., each x can be up to 4
hex digits).
• A series of contiguous zero values in the preferred
format can be abbreviated to ::. Only one instance of
:: can occur in an address. For example, the loopback
address 0:0:0:0:0:0:0:1 can be abbreviated as ::1. The
wildcard address, consisting of all zeros, can be
written as ::.
• An alternate format is useful for expressing IPv4-mapped
IPv6 addresses. This form is written as
x:x:x:x:x:x:d.d.d.d, where the six leading xs are
hexadecimal values that define the six most-significant
16-bit pieces of the address (i.e., 96 bits), and the ds
express a value in dotted-decimal notation that defines
the least significant 32 bits of the address. An
example of such an address is ::FFFF:204.152.189.116.
See RFC 2373 for further details on the representation of
IPv6 addresses.
inet_pton() returns 1 on success (network address was successfully
converted). 0 is returned if src does not contain a character
string representing a valid network address in the specified
address family. If af does not contain a valid address family, -1
is returned and errno is set to EAFNOSUPPORT.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├───────────────────────────────┼───────────────┼────────────────┤
│ inet_pton() │ Thread safety │ MT-Safe locale │
└───────────────────────────────┴───────────────┴────────────────┘
Unlike inet_aton(3) and inet_addr(3), inet_pton() supports IPv6
addresses. On the other hand, inet_pton() accepts only IPv4
addresses in dotted-decimal notation, whereas inet_aton(3) and
inet_addr(3) allow the more general numbers-and-dots notation
(hexadecimal and octal number formats, and formats that don't
require all four bytes to be explicitly written). For an
interface that handles both IPv6 addresses, and IPv4 addresses in
numbers-and-dots notation, see getaddrinfo(3).
POSIX.1-2008.
POSIX.1-2001.
AF_INET6 does not recognize IPv4 addresses. An explicit
IPv4-mapped IPv6 address must be supplied in src instead.
The program below demonstrates the use of inet_pton() and
inet_ntop(3). Here are some example runs:
$ ./a.out i6 0:0:0:0:0:0:0:0
::
$ ./a.out i6 1:0:0:0:0:0:0:8
1::8
$ ./a.out i6 0:0:0:0:0:FFFF:204.152.189.116
::ffff:204.152.189.116
Program source
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
main(int argc, char *argv[])
{
unsigned char buf[sizeof(struct in6_addr)];
int domain, s;
char str[INET6_ADDRSTRLEN];
if (argc != 3) {
fprintf(stderr, "Usage: %s {i4|i6|<num>} string\n", argv[0]);
exit(EXIT_FAILURE);
}
domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :
(strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);
s = inet_pton(domain, argv[2], buf);
if (s <= 0) {
if (s == 0)
fprintf(stderr, "Not in presentation format");
else
perror("inet_pton");
exit(EXIT_FAILURE);
}
if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {
perror("inet_ntop");
exit(EXIT_FAILURE);
}
printf("%s\n", str);
exit(EXIT_SUCCESS);
}
getaddrinfo(3), inet(3), inet_ntop(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
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[email protected]
Linux man-pages 6.15 2025-05-17 inet_pton(3)
Pages that refer to this page: getent(1), getaddrinfo(3), gethostbyname(3), getipnodebyname(3), inet(3), inet_ntop(3), systemd.network(5)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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