inet_pton

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



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.
       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:

              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.

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

       ┌────────────┬───────────────┬────────────────┐
       │Interface   Attribute     Value          │
       ├────────────┼───────────────┼────────────────┤
       │inet_pton() │ Thread safety │ MT-Safe locale │
       └────────────┴───────────────┴────────────────┘
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

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.

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)

COLOPHON
       This page is part of release 5.10 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
       https://www.kernel.org/doc/man-pages/.



Linux                              2020-06-09                       INET_PTON(3)