185 lines
7.5 KiB
HTML
185 lines
7.5 KiB
HTML
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<title>gethostbyaddr</title>
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<basefont size="3"> <a name="gethostbyaddr"></a> <a name="tag_03_225"></a><!-- gethostbyaddr -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_225_01"></a>NAME</h4>
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<blockquote>gethostbyaddr, gethostbyname - network host database functions</blockquote>
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<h4><a name="tag_03_225_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/netdb.h.html">netdb.h</a>><br>
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<br>
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</tt></code></p>
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('OB')">OB</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> struct hostent *gethostbyaddr(const void *</tt><i>addr</i><tt>, socklen_t</tt> <i>len</i><tt>,<br>
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int</tt> <i>type</i><tt>);<br>
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struct hostent *gethostbyname(const char *</tt><i>name</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_225_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>These functions shall retrieve information about hosts. This information is considered to be stored in a database that can be
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accessed sequentially or randomly. Implementation of this database is unspecified. <basefont size="2"></p>
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<dl>
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<dt><b>Note:</b></dt>
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<dd>In many cases it is implemented by the Domain Name System, as documented in RFC 1034, RFC 1035, and
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RFC 1886.</dd>
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</dl>
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<basefont size="3">
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<p>Entries shall be returned in <b>hostent</b> structures.</p>
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<p>The <i>gethostbyaddr</i>() function shall return an entry containing addresses of address family <i>type</i> for the host with
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address <i>addr</i>. The <i>len</i> argument contains the length of the address pointed to by <i>addr</i>. The
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<i>gethostbyaddr</i>() function need not be reentrant. A function that is not required to be reentrant is not required to be
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thread-safe.</p>
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<p>The <i>gethostbyname</i>() function shall return an entry containing addresses of address family AF_INET for the host with name
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<i>name</i>. The <i>gethostbyname</i>() function need not be reentrant. A function that is not required to be reentrant is not
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required to be thread-safe.</p>
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<p>The <i>addr</i> argument of <i>gethostbyaddr</i>() shall be an <b>in_addr</b> structure when <i>type</i> is AF_INET. It contains
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a binary format (that is, not null-terminated) address in network byte order. The <i>gethostbyaddr</i>() function is not guaranteed
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to return addresses of address families other than AF_INET, even when such addresses exist in the database.</p>
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<p>If <i>gethostbyaddr</i>() returns successfully, then the <i>h_addrtype</i> field in the result shall be the same as the
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<i>type</i> argument that was passed to the function, and the <i>h_addr_list</i> field shall list a single address that is a copy
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of the <i>addr</i> argument that was passed to the function.</p>
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<p>The <i>name</i> argument of <i>gethostbyname</i>() shall be a node name; the behavior of <i>gethostbyname</i>() when passed a
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numeric address string is unspecified. For IPv4, a numeric address string shall be in the dotted-decimal notation described in <a
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href="inet_addr.html"><i>inet_addr</i>()</a> .</p>
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<p>If <i>name</i> is not a numeric address string and is an alias for a valid host name, then <i>gethostbyname</i>() shall return
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information about the host name to which the alias refers, and <i>name</i> shall be included in the list of aliases returned.</p>
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</blockquote>
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<h4><a name="tag_03_225_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, these functions shall return a pointer to a <b>hostent</b> structure if the requested entry was
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found, and a null pointer if the end of the database was reached or the requested entry was not found.</p>
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<p>Upon unsuccessful completion, <i>gethostbyaddr</i>() and <i>gethostbyname</i>() shall set <i>h_errno</i> to indicate the
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error.</p>
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</blockquote>
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<h4><a name="tag_03_225_05"></a>ERRORS</h4>
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<blockquote>
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<p>These functions shall fail in the following cases. The <i>gethostbyaddr</i>() and <i>gethostbyname</i>() functions shall set
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<i>h_errno</i> to the value shown in the list below. Any changes to <i>errno</i> are unspecified.</p>
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<dl compact>
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<dt>[HOST_NOT_FOUND]</dt>
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<dd><br>
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No such host is known.</dd>
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<dt>[NO_DATA]</dt>
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<dd>The server recognized the request and the name, but no address is available. Another type of request to the name server for the
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domain might return an answer.</dd>
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<dt>[NO_RECOVERY]</dt>
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<dd><br>
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An unexpected server failure occurred which cannot be recovered.</dd>
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<dt>[TRY_AGAIN]</dt>
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<dd>A temporary and possibly transient error occurred, such as a failure of a server to respond.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_225_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_225_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>gethostbyaddr</i>() and <i>gethostbyname</i>() functions may return pointers to static data, which may be overwritten by
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subsequent calls to any of these functions.</p>
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<p>The <a href="../functions/getaddrinfo.html"><i>getaddrinfo</i>()</a> and <a href=
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"../functions/getnameinfo.html"><i>getnameinfo</i>()</a> functions are preferred over the <i>gethostbyaddr</i>() and
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<i>gethostbyname</i>() functions.</p>
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</blockquote>
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<h4><a name="tag_03_225_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_225_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>The <i>gethostbyaddr</i>() and <i>gethostbyname</i>() functions may be withdrawn in a future version.</p>
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</blockquote>
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<h4><a name="tag_03_225_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="endhostent.html"><i>endhostent</i>()</a> , <a href="endservent.html"><i>endservent</i>()</a> , <a href=
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"gai_strerror.html"><i>gai_strerror</i>()</a> , <a href="getaddrinfo.html"><i>getaddrinfo</i>()</a> , <a href=
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"h_errno.html"><i>h_errno</i>()</a> , <a href="inet_addr.html"><i>inet_addr</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/netdb.h.html"><i><netdb.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_225_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 6. Derived from the XNS, Issue 5.2 specification.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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