INET_NET(3) | Library Functions Manual | INET_NET(3)

# NAME

`inet_net_ntop`, `inet_net_pton` — Internet network number manipulation routines

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

`#include <sys/socket.h>`
`#include <netinet/in.h>`
`#include <arpa/inet.h>`

char *
`inet_net_ntop`(int af, const void *src, int bits, char *dst, size_t size);

int
`inet_net_pton`(int af, const char *src, void *dst, size_t size);

# DESCRIPTION

The `inet_net_ntop`() function converts an Internet network number from network format (usually a struct in_addr or some other binary form, in network byte order) to CIDR presentation format (suitable for external display purposes). The bits argument is the number of bits in src that are the network number. It returns `NULL` if an error occurs (in which case errno will have been set), or it returns a pointer to the destination string.

The `inet_net_pton`() function converts a presentation format Internet network number (that is, printable form as held in a character string) to network format (usually a struct in_addr or some other internal binary representation, in network byte order). It returns the number of bits (either computed based on the class, or specified with /CIDR), or -1 if a failure occurred (in which case errno will have been set).

The currently supported values for af are `AF_INET` and `AF_INET6`. The size argument is the size of the result buffer dst.

# NETWORK NUMBERS (IP VERSION 4)

Internet network numbers may be specified in one of the following forms:

    a.b.c.d/bits
    a.b.c.d
    a.b.c
    a.b
    a

When four parts are specified, each is interpreted as a byte of data and assigned, from left to right, to the four bytes of an Internet network number. Note that when an Internet network number is viewed as a 32-bit integer quantity on a system that uses little-endian byte order (such as the Intel 386, 486, and Pentium processors) the bytes referred to above appear as “`d.c.b.a`”. That is, little-endian bytes are ordered from right to left.

When a three part number is specified, the last part is interpreted as a 16-bit quantity and placed in the rightmost two bytes of the Internet network number. This makes the three part number format convenient for specifying Class B network numbers as “`128.net.host`”.

When a two part number is supplied, the last part is interpreted as a 24-bit quantity and placed in the rightmost three bytes of the Internet network number. This makes the two part number format convenient for specifying Class A network numbers as “`net.host`”.

When only one part is given, the value is stored directly in the Internet network number without any byte rearrangement.

All numbers supplied as “parts” in a ‘`.`’ notation may be decimal, octal, or hexadecimal, as specified in the C language (i.e., a leading 0x or 0X implies hexadecimal; otherwise, a leading 0 implies octal; otherwise, the number is interpreted as decimal).

# ERRORS

The `inet_net_ntop`() and `inet_net_pton`() functions may fail with

[`EAFNOSUPPORT`]
  The value of af was not `AF_INET` or `AF_INET6`.
[`EMSGSIZE`]
  The conversion of src overflows size of dst.

The `inet_net_ntop`() function may fail with

[`EINVAL`]
  The bits argument contains an invalid number of bits for the requested address family.

The `inet_net_pton`() function may fail with

[`ENOENT`]
  The src was not a valid Internet network number.

# SEE ALSO

byteorder(3), inet(3), networks(5)

# HISTORY

The `inet_net_ntop`() and `inet_net_pton`() functions appeared in BIND 4.9.4 and thence NetBSD 1.3. Support for `AF_INET6` appeared in NetBSD 1.6.

July 20, 2012 | NetBSD 11.0