372 lines
11 KiB
HTML
372 lines
11 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>gethostbyname_r()--Get Host Information for Host Name</title>
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Begin Header Records ========================================== -->
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<!-- Unix8 SCRIPT J converted by B2H R4.1 (346) (CMS) by V2KEA304 -->
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<!-- at RCHVMW2 on 17 Feb 1999 at 11:05:09 -->
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<!--End Header Records -->
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<!-- Edited by Kersten Feb 02 -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<a name="Top_Of_Page"></a>
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<!-- Java sync-link -->
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<script type="text/javascript" language="Javascript" src="../rzahg/synch.js">
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</script>
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<h2>gethostbyname_r()--Get Host Information for Host Name</h2>
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<div class="box" style="width: 65%;">
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<br>
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BSD 4.3 Syntax<br>
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<pre>
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#include <netdb.h>
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int gethostbyname_r(char *<em>host_name</em>,
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struct hostent *<em>hostent_struct_addr</em>,
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struct hostent_data *<em>hostent_data_struct_addr</em>)
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</pre>
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<br>
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Service Program Name: QSOSRV2<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<br>
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<div class="box" style="width: 65%;">
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<br>
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<a href="_xopen_source.htm">UNIX 98 Compatible Syntax</a><br>
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<pre>
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#define _XOPEN_SOURCE 520
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#include <netdb.h>
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int gethostbyname_r(const char *<em>host_name</em>,
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struct hostent *<em>hostent_struct_addr</em>,
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struct hostent_data *<em>hostent_data_struct_addr</em>)
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</pre>
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<br>
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Service Program Name: QSOSRV2<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<br>
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<p>The <em>gethostbyname_r()</em> function is used to retrieve information
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about a host.</p>
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<p>There are two versions of the API, as shown above. The base i5/OS API uses
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BSD 4.3 structures and syntax. The other uses syntax and structures compatible
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with the UNIX 98 programming interface specifications. You can select the UNIX
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98 compatible interface with the <a href="_xopen_source.htm">_XOPEN_SOURCE</a>
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macro.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>host_name</strong> (input) </dt>
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<dd>Specifies the pointer to the character string that contains the name of the
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host for which information is to be retrieved.<br>
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<br>
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</dd>
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<dt><strong>hostent_struct_addr</strong> (input/output) </dt>
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<dd>Specifies the pointer to a hostent structure where the results will be
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placed. All results must be referenced through this structure.<br>
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<br>
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</dd>
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<dt><strong>hostent_data_struct_addr</strong> (input/output) </dt>
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<dd>Specifies the pointer to the hostent_data structure, which is used to pass
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and preserve results between function calls. The field host_control_blk in the
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hostent_data structure must be initialized with hexadecimal zeros before its
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initial use. If compatibility with other platforms is required, then the entire
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hostent_data structure must be initialized with hexadecimal zeros before
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initial use.</dd>
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</dl>
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<br>
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<h3>Authorities:</h3>
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<p>Authorization of *R (allow access to the object) to the host aliases file
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specified by the <em>hostaliases</em> environment variable.</p>
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<p>You also need *X authority to each directory in the path of the host aliases
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file.</p>
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<br>
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<h3>Return Value</h3>
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<p>The <em>gethostbyname_r()</em> function returns an integer. Possible values
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are:</p>
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<ul>
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<li>-1 (unsuccessful call)</li>
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<li>0 (successful call)</li>
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</ul>
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<p>The <strong>struct hostent</strong> denoted by <strong><em>
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hostent_struct_addr</em></strong> and <strong>struct
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hostent_data</strong>denoted by <strong><em>
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hostent_data_struct_addr</em></strong> are both defined in <strong>
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<netdb.h></strong>. The structure <strong>struct hostent</strong>is
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defined as:</p>
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<pre>
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struct hostent [
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char *h_name;
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char **h_aliases;
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int h_addrtype;
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int h_length;
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char **h_addr_list;
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];
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#define h_addr h_addr_list[0]
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</pre>
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<p><em>h_name</em> points to the character string that contains the name of the
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host. <em>h_aliases</em> is a pointer to a NULL-terminated list of pointers,
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each of which points to a character string that represents an alternative name
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for the host. <em>h_addrtype</em> contains the address type of the host (for
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example, <samp>af_inet</samp>). <em>h_length</em> contains the size of an
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address in octets (for example, the size of an Internet address is 4 octets).
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<em>h_addr_list</em> is a pointer to a NULL-terminated list of pointers, each
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of which points to a network address (in network byte order) for the host.</p>
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<br>
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<h3>Error Conditions</h3>
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<p>When the <em>gethostbyname_r()</em> function fails, <em>h_errno</em>
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(defined in <strong><netdb.h></strong>) can be set to:</p>
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<dl>
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<dt><em>[HOST_NOT_FOUND]</em></dt>
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<dd>
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<p>The host name specified by the <em>host_name</em> parameter was not
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found.</p>
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</dd>
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<dt><em>[NO_DATA]</em></dt>
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<dd>
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<p>The host name is a valid name, but there is no corresponding IP address.</p>
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</dd>
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<dt><em>[NO_RECOVERY]</em></dt>
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<dd>
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<p>An unrecoverable error has occurred.</p>
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</dd>
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<dt><em>[TRY_AGAIN]</em></dt>
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<dd>
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<p>The local server did not receive a response from an authoritative server. An
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attempt at a later time may succeed.</p>
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</dd>
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</dl>
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<p>When the <em>gethostbyname_r()</em> function fails, <em>errno</em> can be
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set to:</p>
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<dl>
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<dt><em>[EACCES]</em></dt>
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<dd>
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<p>Permission denied. The process does not have the appropriate privileges to
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the host aliases file specified by the <em>HOSTALIASES</em> environment
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variable.</p>
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</dd>
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<dt><em>[EINVAL]</em></dt>
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<dd>
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<p>The hostent_data structure was not initialized with hexadecimal zeros before
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initial use. For corrective action, see the description for structure
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hostent_data.</p>
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</dd>
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</dl>
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<br>
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<h3>Usage Notes</h3>
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<ol>
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<li>The iSeries Navigator or the following CL commands can be used to access
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the host database file:<br>
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<br>
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<ul>
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<li>ADDTCPHTE (Add TCP/IP Host Table Entry)</li>
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<li>RMVTCPHTE (Remove TCP/IP Host Table Entry)</li>
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<li>CHGTCPHTE (Change TCP/IP Host Table Entry)</li>
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<li>RNMTCPHTE (Rename TCP/IP Host Table Entry)</li>
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<li>MRGTCPHT (Merge TCP/IP Host Tables)</li>
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</ul>
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<br>
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</li>
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<li>There are two sources from which host information can be obtained: the
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domain name server and the host database file. The path taken depends on
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whether an IP address is configured for a name server using the iSeries
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Navigator or option 12, Change TCP/IP domain information, on the <strong>
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CFGTCP</strong> menu.
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<p><strong>Note:</strong> A person with a UNIX background would expect this
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information to exist in a file known as <strong>/etc/resolv.conf</strong>. If
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the IP address is found (indicating that the local network is a domain
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network), the <em>gethostbyaddr_r()</em> function will attempt to query the
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domain name server for information about a host. If the query fails, the
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information will be obtained from the host database file. If the name server IP
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address is not found (indicating that local network is a flat network), the
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host database file is used to obtain the address.</p>
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</li>
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<li>If the <em>host_name</em> parameter does specify a domain qualified name,
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the <em>gethostbyaddr_r()</em> function will append a domain name to the
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specified host name, if possible. The domain name that will be appended is
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configured using the iSeries Navigator or <strong>CFGTCP</strong> menu option
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12, Change TCP/IP domain information.<br>
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<br>
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</li>
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<li>When the host information is obtained from the host database file, the file
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is opened and the host information is retrieved (if it exists) from the file.
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The file is then closed only if a <em>sethostent_r()</em> call with a non-zero
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parameter value was not previously done.<br>
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<br>
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</li>
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<li>If a <em>sethostent_r()</em> call with a non-zero parameter value was
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previously done, the <em>gethostbyname_r()</em> routine, when obtaining host
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information from the domain name server, will communicate with the domain name
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server over a connection-oriented transport service (for example, TCP).
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Otherwise, <em>gethostbyname_r()</em> will use a connectionless transport
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service (for example, UDP).<br>
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<br>
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</li>
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<li>A job has a coded character set identifier (CCSID) and a default CCSID. The
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default CCSID is the same as the job CCSID unless the job CCSID specifies
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65535, which requests that no database translation be performed. In this case,
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the default CCSID is set by the system based on the language ID in effect for
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the job.
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<p>If the host information is retrieved from the domain name server, sockets
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converts the host name specified by the <em>host_name</em> parameter to ASCII
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before communicating with the domain name server. If the host information is
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retrieved from the host database file, no conversion is done on the host name
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specified by the <em>host_name</em> parameter unless the CCSID of the job is
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something other than 65535. In addition, host names returned in the hostent
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will be returned in the default CCSID of the job if they are obtained from the
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domain name server. For translation to occur for the host names returned in the
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hostent structure when they are obtained from the host database file, you must
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use a job CCSID of something other than 65535.</p>
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</li>
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<li>Address families are defined in <strong><sys/socket.h></strong>, and
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the <strong>in_addr</strong> structure is defined in <strong>
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<netinet/in.h></strong>.<br>
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<br>
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</li>
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<li><em>gethostbyname_r()</em> will resolve local host aliases to a domain name
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which are then resolved with a query using DNS. See <a href="reshostalias.htm">
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res_hostalias()</a> for more information on aliases.<br>
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<br>
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</li>
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<li>When you develop in C-based languages and an application is compiled with
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the _XOPEN_SOURCE macro defined to the value 520 or greater, the <em>
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gethostbyname_r()</em> API is mapped to <em>qso_gethostbyname_r98()</em>.</li>
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</ol>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li><a href="_xopen_source.htm">_XOPEN_SOURCE</a>--Using _XOPEN_SOURCE for the
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UNIX 98 compatible interface<br>
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<br>
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</li>
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<li><a href="hstrerror.htm">hstrerror()</a>--Retrieve Resolver Error
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Message<br>
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<br>
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</li>
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<li><a href="reshostalias.htm">res_hostalias()</a>--Retrieve the host alias<br>
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<br>
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</li>
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<li><a href="tsehoste.htm">endhostent_r()</a>--Close Host Database<br>
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<br>
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</li>
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<li><a href="tsghosta.htm">gethostbyaddr_r()</a>--Get Host Information for IP
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Address<br>
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<br>
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</li>
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<li><a href="tsghoste.htm">gethostent_r()</a>--Get Next Entry from Host
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Database<br>
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<br>
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</li>
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<li><a href="tsshoste.htm">sethostent_r()</a>--Open Host Database</li>
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</ul>
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<br>
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<hr>
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API introduced: V3R1
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
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</tr>
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</table>
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</center>
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