inet_pton(3) — Linux manual page


inet_pton(3)            Library Functions Manual            inet_pton(3)

NAME         top

       inet_pton - convert IPv4 and IPv6 addresses from text to binary

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <arpa/inet.h>

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

DESCRIPTION         top

       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:

              •  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

              See RFC 2373 for further details on the representation of
              IPv6 addresses.

RETURN VALUE         top

       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         top

       For an explanation of the terms used in this section, see
       │ Interface                    Attribute     Value          │
       │ inet_pton()                  │ Thread safety │ MT-Safe locale │

VERSIONS         top

       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         top


HISTORY         top


BUGS         top

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

EXAMPLES         top

       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);


SEE ALSO         top

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

Linux man-pages (unreleased)     (date)                     inet_pton(3)

Pages that refer to this page: getent(1)getaddrinfo(3)gethostbyname(3)getipnodebyname(3)inet(3)inet_ntop(3)