inet_pton(3) Library Functions Manual inet_pton(3)
NAME
inet_pton - convert IPv4 and IPv6 addresses from text to binary form
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <arpa/inet.h>
int inet_pton(int af, const char *restrict src, void *restrict 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.
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 ad-
dress 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 ad-
dress. 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 ad-
dress, 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 nota-
tion that defines the least significant 32 bits of the ad-
dress. 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 con-
verted). 0 is returned if src does not contain a character string rep-
resenting 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌────────────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────┼───────────────┼────────────────┤
│ inet_pton() │ Thread safety │ MT-Safe locale │
└────────────────────────────────────┴───────────────┴────────────────┘
VERSIONS
Unlike inet_aton(3) and inet_addr(3), inet_pton() supports IPv6 ad-
dresses. 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 num-
ber formats, and formats that don't require all four bytes to be ex-
plicitly written). For an interface that handles both IPv6 addresses,
and IPv4 addresses in numbers-and-dots notation, see getaddrinfo(3).
STANDARDS
POSIX.1-2008.
HISTORY
POSIX.1-2001.
BUGS
AF_INET6 does not recognize IPv4 addresses. An explicit IPv4-mapped
IPv6 address must be supplied in src instead.
EXAMPLES
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)
Linux man-pages 6.7 2023-10-31 inet_pton(3)
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