INET_NET(3) BSD Library Functions Manual INET_NET(3)NAME
inet_net_ntop, inet_net_pton — Internet network number manipulation rou‐
Standard C Library (libc, -lc)
inet_net_ntop(int af, const void *src, int bits, char *dst, size_t size);
inet_net_pton(int af, const char *src, void *dst, size_t size);
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 a system error occurs (in
which case, errno will have been set), or it returns a pointer to the
The inet_net_pton() function converts a presentation format Internet net‐
work 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. It will be set
to ENOENT if the Internet network number was not valid).
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:
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
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).
SEE ALSObyteorder(3), inet(3), networks(5)HISTORY
The inet_net_ntop() and inet_net_pton() functions appeared in BIND 4.9.4.
BSD February 26, 2006 BSD