inet_pton(3) — Linux manual page


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

NAME         top

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

SYNOPSIS         top

       #include <arpa/inet.h>

       int inet_pton(int af, const char *src, void *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:

              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

              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:

              See RFC 2373 for further details on the representation of IPv6

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 │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

NOTES         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).

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)

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2020-06-09                     INET_PTON(3)

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