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 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:

              •  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 address,
                 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 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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │Interface                                               │ Attribute     │ Value          │
       ├────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │inet_pton()                                             │ Thread safety │ MT-Safe locale │
       └────────────────────────────────────────────────────────┴───────────────┴────────────────┘

VERSIONS

       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).

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)