77 lines
5.6 KiB
HTML
77 lines
5.6 KiB
HTML
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<meta name="DC.Title" content="File descriptor" />
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<meta name="abstract" content="When using ILE C/400 stream I/O functions as defined by the American National Standards Institute (ANSI) to perform operations on a file, you identify the file through use of pointers. When using the integrated file system C functions, you identify the file by specifying a file descriptor. A file descriptor is a positive integer that must be unique in each job." />
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<meta name="DC.subject" content="integrated file system, programming interfaces, pointers and file descriptors, pointers, file descriptor, open file description" />
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<title>File descriptor</title>
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<body id="rzaaxfildes"><a name="rzaaxfildes"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">File descriptor</h1>
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<div><p>When using ILE C/400<sup>®</sup> stream I/O functions as defined by the American
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National Standards Institute (ANSI) to perform operations on a file, you identify
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the file through use of pointers. When using the integrated file system C
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functions, you identify the file by specifying a file descriptor. A <dfn class="term">file
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descriptor</dfn> is a positive integer that must be unique in each job.</p>
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<div class="section"><p>The job uses a file descriptor to identify an open file when performing
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operations on the file. The file descriptor is represented by the variable <em>fildes</em> in
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C functions that operate on the integrated file system and by the variable <em>descriptor</em> in
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C functions that operate on sockets.</p>
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</div>
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<div class="section"><p>Each file descriptor refers to an <dfn class="term">open
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file description</dfn>, which contains information such as a file offset,
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status of the file, and access modes for the file. The same open file description
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can be referred to by more than one file descriptor, but a file descriptor
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can refer to only one open file description.</p>
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</div>
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<div class="example"> <div class="fignone"><span class="figcap">Figure 1. File descriptor and open file description</span><br /><img src="rv3n077.gif" alt="File descriptor and open file description" /><br /></div>
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</div>
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<div class="section"><p>If an ILE C/400 stream I/O function is used with the integrated
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file system, the ILE C/400 run-time support converts the file pointer to
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a file descriptor.</p>
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</div>
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<div class="section"><p>When using the <span class="q">"root"</span> (/), QOpenSys, or user-defined file
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systems, you can pass access to an open file description from one job to another,
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thus allowing the job to access the file. You do this by using the <span class="apiname">givedescriptor()</span> or <span class="apiname">takedescriptor()</span> function
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to pass the file descriptor between jobs. </p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaaxprogapi.htm" title="Many of the application program interfaces (APIs) that perform operations on integrated file system objects are in the form of C language functions.">Perform operations using APIs</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../apis/gvsoc.htm">givedescriptor() API</a></div>
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<div><a href="../apis/tksoc.htm">takedescriptor() API</a></div>
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<div><a href="../rzab6/rzab6soxoverview.htm">Sockets programming</a></div>
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<div><a href="../apis/unix8.htm">Sockets APIs</a></div>
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