1INET_ADDR(3P) POSIX Programmer's Manual INET_ADDR(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 inet_addr, inet_ntoa — IPv4 address manipulation
13
15 #include <arpa/inet.h>
16 in_addr_t inet_addr(const char *cp);
18 char *inet_ntoa(struct in_addr in);
19
21 The inet_addr() function shall convert the string pointed to by cp, in
22 the standard IPv4 dotted decimal notation, to an integer value suitable
23 for use as an Internet address.
24 The inet_ntoa() function shall convert the Internet host address speci‐
26 fied by in to a string in the Internet standard dot notation.
27 The inet_ntoa() function need not be thread-safe.
29 All Internet addresses shall be returned in network order (bytes
31 ordered from left to right).
32 Values specified using IPv4 dotted decimal notation take one of the
34 following forms:
35 a.b.c.d When four parts are specified, each shall be interpreted as a
37 byte of data and assigned, from left to right, to the four
38 bytes of an Internet address.
39 a.b.c When a three-part address is specified, the last part shall
41 be interpreted as a 16-bit quantity and placed in the right‐
42 most two bytes of the network address. This makes the three-
43 part address format convenient for specifying Class B network
44 addresses as "128.net.host".
45 a.b When a two-part address is supplied, the last part shall be
47 interpreted as a 24-bit quantity and placed in the rightmost
48 three bytes of the network address. This makes the two-part
49 address format convenient for specifying Class A network
50 addresses as "net.host".
51 a When only one part is given, the value shall be stored
53 directly in the network address without any byte rearrange‐
54 ment.
55 All numbers supplied as parts in IPv4 dotted decimal notation may be
57 decimal, octal, or hexadecimal, as specified in the ISO C standard
58 (that is, a leading 0x or 0X implies hexadecimal; otherwise, a leading
59 '0' implies octal; otherwise, the number is interpreted as decimal).
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62 Upon successful completion, inet_addr() shall return the Internet
63 address. Otherwise, it shall return (in_addr_t)(-1).
64 The inet_ntoa() function shall return a pointer to the network address
66 in Internet standard dot notation.
67
69 No errors are defined.
70 The following sections are informative.
72
74 None.
75
77 The return value of inet_ntoa() may point to static data that may be
78 overwritten by subsequent calls to inet_ntoa().
79
81 None.
82
84 None.
85
87 endhostent(), endnetent()
88 The Base Definitions volume of POSIX.1‐2017, <arpa_inet.h>
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92 Portions of this text are reprinted and reproduced in electronic form
93 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
94 table Operating System Interface (POSIX), The Open Group Base Specifi‐
95 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
96 Electrical and Electronics Engineers, Inc and The Open Group. In the
97 event of any discrepancy between this version and the original IEEE and
98 The Open Group Standard, the original IEEE and The Open Group Standard
99 is the referee document. The original Standard can be obtained online
100 at http://www.opengroup.org/unix/online.html .
101 Any typographical or formatting errors that appear in this page are
103 most likely to have been introduced during the conversion of the source
104 files to man page format. To report such errors, see https://www.ker‐
105 nel.org/doc/man-pages/reporting_bugs.html .
106IEEE/The Open Group 2017 INET_ADDR(3P)