The inet_addr() function shall convert the string pointed to by
cp, in the standard IPv4 dotted decimal notation, to an integer value
suitable for use as an Internet address.
The inet_ntoa() function shall convert the Internet host address
specified by in to a string in the Internet standard dot notation.
The inet_ntoa() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
All Internet addresses shall be returned in network order (bytes ordered from
left to right).
Values specified using IPv4 dotted decimal notation take one of the following
When four parts are specified, each shall be interpreted as
a byte of data and assigned, from left to right, to the four bytes of an
When a three-part address is specified, the last part shall
be interpreted as a 16-bit quantity and placed in the rightmost two bytes
of the network address. This makes the three-part address format
convenient for specifying Class B network addresses as
When a two-part address is supplied, the last part shall be
interpreted as a 24-bit quantity and placed in the rightmost three bytes
of the network address. This makes the two-part address format convenient
for specifying Class A network addresses as "net.host"
When only one part is given, the value shall be stored
directly in the network address without any byte rearrangement.
All numbers supplied as parts in IPv4 dotted decimal notation may be decimal,
octal, or hexadecimal, as specified in the ISO C standard (that is, a
leading 0x or 0X implies hexadecimal; otherwise, a leading '0' implies
octal; otherwise, the number is interpreted as decimal).
Upon successful completion, inet_addr() shall return the Internet
address. Otherwise, it shall return ( in_addr_t)(-1).
The inet_ntoa() function shall return a pointer to the network address in
Internet standard dot notation.
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