inet_pton

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.
       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:

              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 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 ::.

              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  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  at-
       tributes(7).

       +------------+---------------+----------------+
       |Interface   | Attribute     | Value          |
       +------------+---------------+----------------+
       |inet_pton() | Thread safety | MT-Safe locale |
       +------------+---------------+----------------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

NOTES
       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).

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 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

Linux                             2019-03-06                      INET_PTON(3)