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 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 (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

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