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INET_PTON(3) Linux Programmer's Manual INET_PTON(3)
NAME
inet_pton - convert IPv4 and IPv6 addresses from text to binary form
SYNOPSIS
#include <arpa/inet.h>
int inet_pton(int af, const char *src, void *dst);
DESCRIPTION
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.
The following address families are currently supported:
AF_INET
src points to a character string containing an IPv4 network address in dot-
ted-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:
1. 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).
2. A series of contiguous zero values in the preferred format can be abbre-
viated 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 zeroes, can be written as ::.
3. 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.
RETURN VALUE
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.
CONFORMING TO
POSIX.1-2001.
NOTES
Unlike inet_aton(3) and inet_addr(3), inet_pton() supports IPv6 addresses. On the
other hand, inet_pton() only accepts IPv4 addresses in dotted-decimal notation,
whereas inet_aton(3) and inet_addr(3) allow the more general numbers-and-dots nota-
tion (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).
BUGS
AF_INET6 does not recognize IPv4 addresses. An explicit IPv4-mapped IPv6 address
must be supplied in src instead.
EXAMPLE
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);
}
SEE ALSO
getaddrinfo(3), inet(3), inet_ntop(3)
COLOPHON
This page is part of release 3.22 of the Linux man-pages project. A description of
the project, and information about reporting bugs, can be found at http://www.ker-
nel.org/doc/man-pages/.
Linux 2008-06-18 INET_PTON(3)
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