The inet_ntop() function shall convert a numeric address into a text
string suitable for presentation. The af argument shall specify the
family of the address. This can be AF_INET or AF_INET6. The src
argument points to a buffer holding an IPv4 address if the af argument
is AF_INET, or an IPv6 address if the af argument is AF_INET6;
the address must be in network byte order. The dst argument points to a
buffer where the function stores the resulting text string; it shall not be
NULL. The size argument specifies the size of this buffer, which shall
be large enough to hold the text string (INET_ADDRSTRLEN characters for IPv4,
INET6_ADDRSTRLEN characters for IPv6).
The inet_pton() function shall convert an address in its standard text
presentation form into its numeric binary form. The af argument shall
specify the family of the address. The AF_INET and AF_INET6 address
families shall be supported. The src argument points to the string
being passed in. The dst argument points to a buffer into which the
function stores the numeric address; this shall be large enough to hold the
numeric address (32 bits for AF_INET, 128 bits for AF_INET6).
If the af argument of inet_pton() is AF_INET, the src
string shall be in the standard IPv4 dotted-decimal form:
where "ddd" is a one to three digit decimal number between 0
and 255 (see inet_addr() ). The inet_pton() function does not
accept other formats (such as the octal numbers, hexadecimal numbers, and
fewer than four numbers that inet_addr() accepts).
If the af argument of inet_pton() is AF_INET6, the src
string shall be in one of the following standard IPv6 text forms:
The preferred form is "x:x:x:x:x:x:x:x" ,
where the 'x' s are the hexadecimal values of the eight 16-bit
pieces of the address. Leading zeros in individual fields can be omitted,
but there shall be at least one numeral in every field.
A string of contiguous zero fields in the preferred form
can be shown as "::" . The "::" can only
appear once in an address. Unspecified addresses (
"0:0:0:0:0:0:0:0" ) may be represented simply as
A third form that is sometimes more convenient when dealing
with a mixed environment of IPv4 and IPv6 nodes is
"x:x:x:x:x:x:d.d.d.d" , where the 'x' s are the
hexadecimal values of the six high-order 16-bit pieces of the address, and
the 'd' s are the decimal values of the four low-order 8-bit pieces
of the address (standard IPv4 representation).
A more extensive description of the standard
representations of IPv6 addresses can be found in RFC 2373.
The inet_ntop() function shall return a pointer to the buffer containing
the text string if the conversion succeeds, and NULL otherwise, and set
errno to indicate the error.
The inet_pton() function shall return 1 if the conversion succeeds, with
the address pointed to by dst in network byte order. It shall return 0
if the input is not a valid IPv4 dotted-decimal string or a valid IPv6
address string, or -1 with errno set to [EAFNOSUPPORT] if the af
argument is unknown.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html