INET_PTON(3)               Linux Programmer's Manual              INET_PTON(3)

       inet_pton - convert IPv4 and IPv6 addresses from text to binary form

       #include <arpa/inet.h>

       int inet_pton(int af, const char *src, void *dst);

       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:

              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.

              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  nota-
                 tion  that  defines  the  least  significant  32  bits of the
                 address.    An   example    of    such    an    address    is

              See  RFC  2373 for further details on the representation of IPv6

       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.

       For  an  explanation  of  the  terms  used   in   this   section,   see

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

       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  num-
       ber  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 getad-

       AF_INET6 does not recognize IPv4 addresses.   An  explicit  IPv4-mapped
       IPv6 address must be supplied in src instead.

       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
           $ ./a.out i6 0:0:0:0:0:FFFF:

   Program source

       #include <arpa/inet.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       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]);

           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");

           if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {


           printf("%s\n", str);


       getaddrinfo(3), inet(3), inet_ntop(3)

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Linux                             2017-09-15                      INET_PTON(3)
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