Go Back    


Recursive Search Engine for Linux and Unix Man Pages by Neo
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)

INET(3) 			    Linux Programmer's Manual				  INET(3)

NAME
       inet_aton,  inet_addr,  inet_network,  inet_ntoa,  inet_makeaddr, inet_lnaof, inet_netof -
       Internet address manipulation routines

SYNOPSIS
       #include <sys/socket.h>
       #include <netinet/in.h>
       #include <arpa/inet.h>

       int inet_aton(const char *cp, struct in_addr *inp);

       in_addr_t inet_addr(const char *cp);

       in_addr_t inet_network(const char *cp);

       char *inet_ntoa(struct in_addr in);

       struct in_addr inet_makeaddr(int net, int host);

       in_addr_t inet_lnaof(struct in_addr in);

       in_addr_t inet_netof(struct in_addr in);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       inet_aton(), inet_ntoa(): _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       inet_aton() converts the Internet host address cp from the IPv4 numbers-and-dots  notation
       into  binary  form  (in network byte order) and stores it in the structure that inp points
       to.  inet_aton() returns nonzero if the address is valid, zero if not.  The  address  sup-
       plied in cp can have one of the following forms:

       a.b.c.d	 Each  of  the	four numeric parts specifies a byte of the address; the bytes are
		 assigned in left-to-right order to produce the binary address.

       a.b.c	 Parts a and b specify the first two bytes of the  binary  address.   Part  c  is
		 interpreted as a 16-bit value that defines the rightmost two bytes of the binary
		 address.  This notation is suitable for specifying (outmoded)	Class  B  network
		 addresses.

       a.b	 Part a specifies the first byte of the binary address.  Part b is interpreted as
		 a 24-bit value that defines the rightmost three bytes	of  the  binary  address.
		 This notation is suitable for specifying (outmoded) Class C network addresses.

       a	 The  value  a	is interpreted as a 32-bit value that is stored directly into the
		 binary address without any byte rearrangement.

       In all of the above forms, components of the dotted address can be specified  in  decimal,
       octal  (with  a leading 0), or hexadecimal, with a leading 0X).	Addresses in any of these
       forms are collectively termed IPV4 numbers-and-dots notation.  The form that uses  exactly
       four  decimal  numbers  is referred to as IPv4 dotted-decimal notation (or sometimes: IPv4
       dotted-quad notation).

       The inet_addr() function converts the Internet host address cp from IPv4  numbers-and-dots
       notation  into  binary  data  in network byte order.  If the input is invalid, INADDR_NONE
       (usually -1) is returned.  Use of this function is  problematic	because  -1  is  a  valid
       address (255.255.255.255).  Avoid its use in favor of inet_aton(), inet_pton(3), or getad-
       drinfo(3) which provide a cleaner way to indicate error return.

       The inet_network() function converts cp, a string in IPv4 numbers-and-dots notation,  into
       a  number in host byte order suitable for use as an Internet network address.  On success,
       the converted address is returned.  If the input is invalid, -1 is returned.

       The inet_ntoa() function converts the Internet host address  in,  given	in  network  byte
       order,  to  a  string in IPv4 dotted-decimal notation.  The string is returned in a stati-
       cally allocated buffer, which subsequent calls will overwrite.

       The inet_lnaof() function returns the local network address part of the	Internet  address
       in.  The returned value is in host byte order.

       The inet_netof() function returns the network number part of the Internet address in.  The
       returned value is in host byte order.

       The inet_makeaddr() function is the converse of inet_netof() and inet_lnaof().  It returns
       an  Internet  host  address in network byte order, created by combining the network number
       net with the local address host, both in host byte order.

       The  structure  in_addr	as  used  in  inet_ntoa(),  inet_makeaddr(),   inet_lnaof()   and
       inet_netof() is defined in <netinet/in.h> as:

	   typedef uint32_t in_addr_t;

	   struct in_addr {
	       in_addr_t s_addr;
	   };

CONFORMING TO
       4.3BSD.	 inet_addr()  and  inet_ntoa() are specified in POSIX.1-2001.  inet_aton() is not
       specified in POSIX.1-2001, but is available on most systems.

NOTES
       On the i386 the host byte order is Least Significant Byte first (little	endian),  whereas
       the  network  byte  order,  as  used  on the Internet, is Most Significant Byte first (big
       endian).

       inet_lnaof(), inet_netof(), and inet_makeaddr() are legacy functions that assume they  are
       dealing	with  classful	network  addresses.   Classful	networking  divides  IPv4 network
       addresses into host and network components at byte boundaries, as follows:

       Class A	 This address type is indicated by the value 0 in the most significant bit of the
		 (network  byte  ordered)  address.  The network address is contained in the most
		 significant byte, and the host address occupies the remaining three bytes.

       Class B	 This address type is indicated by the binary value 10 in  the	most  significant
		 two  bits of the address.  The network address is contained in the two most sig-
		 nificant bytes, and the host address occupies the remaining two bytes.

       Class C	 This address type is indicated by the binary value 110 in the	most  significant
		 three	bits  of the address.  The network address is contained in the three most
		 significant bytes, and the host address occupies the remaining byte.

       Classful network addresses are now obsolete, having been superseded  by	Classless  Inter-
       Domain  Routing	(CIDR), which divides addresses into network and host components at arbi-
       trary bit (rather than byte) boundaries.

EXAMPLE
       An example of the use of inet_aton() and inet_ntoa() is shown below.  Here are some  exam-
       ple runs:

	   $ ./a.out 226.000.000.037	  # Last byte is in octal
	   226.0.0.31
	   $ ./a.out 0x7f.1		  # First byte is in hex
	   127.0.0.1

   Program source

       #define _BSD_SOURCE
       #include <arpa/inet.h>
       #include <stdio.h>
       #include <stdlib.h>

       int
       main(int argc, char *argv[])
       {
	   struct in_addr addr;

	   if (argc != 2) {
	       fprintf(stderr, "%s <dotted-address>\n", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   if (inet_aton(argv[1], &addr) == 0) {
	       fprintf(stderr, "Invalid address\n");
	       exit(EXIT_FAILURE);
	   }

	   printf("%s\n", inet_ntoa(addr));
	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       byteorder(3),	 getaddrinfo(3),    gethostbyname(3),	 getnameinfo(3),    getnetent(3),
       inet_ntop(3), inet_pton(3), hosts(5), networks(5)

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

GNU					    2013-02-10					  INET(3)
The UNIX and Linux Forums Man Pages : 2014 The UNIX and Linux Forums


All times are GMT -4. The time now is 10:54 PM.