341 lines
11 KiB
HTML
341 lines
11 KiB
HTML
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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>gethostbyaddr_r()--Get Host Information for IP Address</title>
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<h2>gethostbyaddr_r()--Get Host Information for IP Address</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 gethostbyaddr_r(char *<em>host_address</em>,
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int <em>address_length</em>,
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int <em>address_type</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 gethostbyaddr_r(const void *<em>host_address</em>,
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socklen_t <em>address_length</em>,
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int <em>address_type</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>gethostbyaddr_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 BSD
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4.3 structures and syntax. The other uses syntax and structures compatible with the
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UNIX 98 programming interface specifications. You can select the UNIX 98 compatible
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interface with the <a href="_xopen_source.htm">_XOPEN_SOURCE</a> macro.</p>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>host_address</strong> (input) </dt>
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<dd>Specifies the pointer to a structure of type <strong>in_addr</strong> that
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contains the address of the 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>address_length</strong> (input) </dt>
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<dd>Specifies the length of the <em>host_address</em>.<br>
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<br>
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</dd>
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<dt><strong>address_type</strong> (input) </dt>
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<dd>Specifies the domain type of the host address. Currently, <samp>af_inet</samp>
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is the only value for this parameter that is supported.<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 initialized with hexadecimal zeros before initial
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use.</dd>
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</dl>
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<br>
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<h3>Authorities</h3>
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<p>No authorization is required.</p>
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<br>
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<h3>Return Value</h3>
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<p>The <em>gethostbyaddr_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)
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<p>The <strong>struct hostent</strong> denoted by
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<strong><em>hostent_struct_addr</em></strong> and <strong>struct
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hostent_data</strong>denoted by
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<strong><em>hostent_data_struct_addr</em></strong> are both defined in
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<strong><netdb.h></strong>. The structure <strong>struct
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hostent</strong>is 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 address
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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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</li>
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</ul>
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<br>
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<h3>Error Conditions</h3>
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<p>When the <em>gethostbyaddr_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><p>The host name specified by the
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<em>host_address</em> parameter was not found.</p></dd>
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<dt><em>[NO_DATA]</em></dt>
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<dd><p>The host name is a valid name, but there is no
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corresponding IP address.</p></dd>
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<dt><em>[NO_RECOVERY]</em></dt>
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<dd><p>An unrecoverable error has occurred.</p></dd>
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<dt><em>[TRY_AGAIN]</em></dt>
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<dd><p>The local server did not receive a response from
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an authoritative server. An attempt at a later time may succeed.</p></dd>
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</dl>
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<p>When the <em>gethostbyaddr_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>[EINVAL]</em></dt>
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<dd><p>The hostent_data structure was not properly
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initialized with hexadecimal zeros before initial use. For corrective action,
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see the description for structure hostent_data.</p></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
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used to access the host database file:<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 Navigator or
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option 12, Change TCP/IP domain information, on the <strong>CFGTCP</strong> menu.
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<p><strong>Note:</strong> A person with a UNIX background would expect this information to
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exist in a file known as <strong>/etc/resolv.conf</strong>. If the IP address
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is found (indicating that the local network is a domain network), the
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<em>gethostbyaddr_r()</em> function will attempt to query the domain name
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server for information about a host. If the query fails, the information will
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be obtained from the host database file. If the name server IP address is not
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found (indicating that local network is a flat network), the host database file
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is used to obtain the host information.
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</p>
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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>gethostbyaddr_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>gethostbyaddr_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>If the host information is obtained from the domain name server, the
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information is returned in the default coded character set identifier (CCSID)
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currently in effect for the job. (The default CCSID is the same as the job
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CCSID unless 65535 is requested, in which case the default CCSID is set based
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on the language ID of the job. See the <a href=
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"../nls/rbagsglobalmain.htm">globalization</a> topic for more information.) If
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the host information is retrieved from the host database file the default CCSID
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of the job is not used. To request translation of the host information when it
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is retrieved from the host database file, you must use a job CCSID of something
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other than 65535.<br>
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<br>
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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
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<strong><netinet/in.h></strong>.<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 the _XOPEN_SOURCE
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macro defined to the value 520 or greater, the <em>gethostbyaddr_r()</em> API is mapped to
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<em>qso_gethostbyaddr_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="tsghostb.htm">gethostbyname_r()</a>--Get Host Information for Host
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Name<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="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="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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<tr align="center">
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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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</body>
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</html>
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