INET_ADDR(3P) POSIX Programmer's Manual INET_ADDR(3P)PROLOG
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 speci‐
fied 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 right‐
most 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 rearrange‐
ment.
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 ALSOendhostent(), endnetent()
The Base Definitions volume of POSIX.1‐2008, <arpa_inet.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 INET_ADDR(3P)
