INET_ADDR
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
inet_addr,
inet_ntoa
--- IPv4 address manipulation
SYNOPSIS
#include <arpa/inet.h>
in_addr_t inet_addr(const char *cp);
char *inet_ntoa(struct in_addr in);
DESCRIPTION
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 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 forms:
- a.b.c.d
-
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 Internet
address.
- a.b.c
-
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
"128.net.host".
- a.b
-
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".
- a
-
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).
RETURN VALUE
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.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The return value of
inet_ntoa()
may point to static data that may be overwritten by subsequent calls to
inet_ntoa().
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
endhostent(),
endnetent()
The Base Definitions volume of POSIX.1-2017,
<arpa_inet.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .