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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  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:

              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 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-signif-
                 icant 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 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).

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 informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-06-18                      INET_PTON(3)