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INET_ADDR(3P)              POSIX Programmer's Manual             INET_ADDR(3P)

       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

       inet_addr, inet_ntoa - IPv4 address manipulation

       #include <arpa/inet.h>

       in_addr_t inet_addr(const char *cp);
       char *inet_ntoa(struct in_addr in);

       The  inet_addr()  function shall convert the string pointed to by cp, in the standard IPv4 dotted decimal nota-
       tion, 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 forms:

              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  con-
              venient for specifying Class B network addresses as "" .

       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 "" .

       a      When  only one part is given, the value shall be stored directly in the network address without any byte

       All numbers supplied as parts in IPv4 dotted decimal notation may be decimal, octal, or hexadecimal, as  speci-
       fied  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  (

       The inet_ntoa() function shall return a pointer to the network address in Internet standard dot notation.

       No errors are defined.

       The following sections are informative.


       The  return  value  of  inet_ntoa()  may  point  to  static data that may be overwritten by subsequent calls to



       endhostent(), endnetent(), the Base Definitions volume of IEEE Std 1003.1-2001, <arpa/inet.h>

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at .

IEEE/The Open Group                  2003                        INET_ADDR(3P)