1GETHOSTBYADDR(3P)          POSIX Programmer's Manual         GETHOSTBYADDR(3P)
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PROLOG

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.
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NAME

12       gethostbyaddr, gethostbyname - network host database functions
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SYNOPSIS

15       #include <netdb.h>
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19       struct hostent *gethostbyaddr(const void *addr, socklen_t len,
20              int type);
21       struct hostent *gethostbyname(const char *name);
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DESCRIPTION

25       These functions shall retrieve information about hosts.  This  informa‐
26       tion  is  considered  to  be  stored in a database that can be accessed
27       sequentially or randomly. Implementation of this database  is  unspeci‐
28       fied.
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30       Note:  In  many  cases  it is implemented by the Domain Name System, as
31              documented in RFC 1034, RFC 1035, and RFC 1886.
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34       Entries shall be returned in hostent structures.
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36       The gethostbyaddr() function shall return an entry containing addresses
37       of address family type for the host with address addr. The len argument
38       contains the length of the address pointed to  by  addr.  The  gethost‐
39       byaddr()  function  need  not  be  reentrant.  A  function  that is not
40       required to be reentrant is not required to be thread-safe.
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42       The gethostbyname() function shall return an entry containing addresses
43       of  address  family AF_INET for the host with name name. The gethostby‐
44       name() function need not be reentrant.  A function that is not required
45       to be reentrant is not required to be thread-safe.
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47       The addr argument of gethostbyaddr() shall be an in_addr structure when
48       type is AF_INET. It contains a binary format (that is, not  null-termi‐
49       nated)  address  in network byte order. The gethostbyaddr() function is
50       not guaranteed to return  addresses  of  address  families  other  than
51       AF_INET, even when such addresses exist in the database.
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53       If  gethostbyaddr()  returns successfully, then the h_addrtype field in
54       the result shall be the same as the type argument that  was  passed  to
55       the  function,  and  the  h_addr_list field shall list a single address
56       that is a copy of the addr argument that was passed to the function.
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58       The name argument of gethostbyname() shall be a node name; the behavior
59       of gethostbyname() when passed a numeric address string is unspecified.
60       For IPv4, a numeric address string shall be in the dotted-decimal nota‐
61       tion described in inet_addr() .
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63       If  name  is  not  a numeric address string and is an alias for a valid
64       host name, then gethostbyname() shall return information about the host
65       name  to which the alias refers, and name shall be included in the list
66       of aliases returned.
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RETURN VALUE

69       Upon successful completion, these functions shall return a pointer to a
70       hostent  structure if the requested entry was found, and a null pointer
71       if the end of the database was reached or the requested entry  was  not
72       found.
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74       Upon unsuccessful completion, gethostbyaddr() and gethostbyname() shall
75       set h_errno to indicate the error.
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ERRORS

78       These functions shall fail in the following cases. The  gethostbyaddr()
79       and  gethostbyname()  functions shall set h_errno to the value shown in
80       the list below. Any changes to errno are unspecified.
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82       HOST_NOT_FOUND
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84              No such host is known.
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86       NO_DATA
87              The server recognized the request and the name, but  no  address
88              is available. Another type of request to the name server for the
89              domain might return an answer.
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91       NO_RECOVERY
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93              An unexpected server failure occurred which cannot be recovered.
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95       TRY_AGAIN
96              A temporary and possibly transient error  occurred,  such  as  a
97              failure of a server to respond.
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100       The following sections are informative.
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EXAMPLES

103       None.
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APPLICATION USAGE

106       The  gethostbyaddr()  and gethostbyname() functions may return pointers
107       to static data, which may be overwritten by subsequent calls to any  of
108       these functions.
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110       The  getaddrinfo()  and  getnameinfo() functions are preferred over the
111       gethostbyaddr() and gethostbyname() functions.
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RATIONALE

114       None.
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FUTURE DIRECTIONS

117       The gethostbyaddr() and gethostbyname() functions may be withdrawn in a
118       future version.
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SEE ALSO

121       endhostent(),  endservent(),  gai_strerror(), getaddrinfo(), h_errno(),
122       inet_addr(),  the  Base  Definitions  volume  of  IEEE Std 1003.1-2001,
123       <netdb.h>
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COPYRIGHT

126       Portions  of  this text are reprinted and reproduced in electronic form
127       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
128       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
129       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
130       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
131       event of any discrepancy between this version and the original IEEE and
132       The  Open Group Standard, the original IEEE and The Open Group Standard
133       is the referee document. The original Standard can be  obtained  online
134       at http://www.opengroup.org/unix/online.html .
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138IEEE/The Open Group                  2003                    GETHOSTBYADDR(3P)