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-deci‐
              mal 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  fol‐
              low these rules:

              1. The  preferred format is x:x:x:x:x:x:x:x.  This form consists of eight hexadeci‐
                 mal 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, con‐
                 sisting 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 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()  accepts  only  IPv4  addresses  in  dotted-decimal  notation,  whereas
       inet_aton(3) and inet_addr(3) allow the more general numbers-and-dots notation  (hexadeci‐
       mal  and octal number formats, and formats that don't require all four bytes to be explic‐
       itly 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 3.74 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 http://www.kernel.org/doc/man-pages/.



Linux                                       2008-06-18                               INET_PTON(3)