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<html><!-- #BeginTemplate "/Templates/tmpl.dwt" --><!-- DW6 --><head><!-- #BeginEditable "doctitle" --> <title>PTypes: streams: iobase</title><!-- #EndEditable --> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link rel="stylesheet" href="styles.css"></head><body bgcolor="#FFFFFF" leftmargin="40" marginwidth="40"><p><a href="../index.html"><img src="title-20.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.0" border="0"></a> <hr size="1" noshade><!-- #BeginEditable "body" --> <p class="hpath"><a href="index.html">Top</a>: <a href="streams.html">Streams</a>: iobase </p><blockquote> <pre class="lang">#include <pstreams.h>typedef void (*iostatusevent)(iobase* sender, int code);class iobase { void open(); void close(); void cancel(); int tell(); int seek(int newpos, ioseekmode mode = IO_BEGIN); string get_streamname(); bool get/set_active(bool); bool get/set_cancelled(bool); int get/set_bufsize(int); int get_status(); iostatusevent get/set_onstatus(<span class="def">iostatusevent</span>);}</pre></blockquote><p>The methods and properties of this abstract class are common to all stream interfaces in PTypes.</p><p><span class="def">void iobase::open()</span> opens (activates) the stream.</p><p><span class="def">void iobase::close()</span> closes (deactivates) the stream. This method is called automatically during destruction of an object. <span class="lang">Close()</span> calls <span class="lang">flush()</span> for output streams. To simplify error handling in user programs, this method never throws exceptions. If you want to check for errors during the last write operation, call <span class="lang">flush()</span> explicitly before closing the stream.</p><p><span class="def">void iobase::cancel()</span> closes the stream and sets the <span class="lang">cancelled</span> property to true. In communication streams this method may close the connection immediately, unlike <span class="lang">close()</span>, which always tries to flush data buffers and then close the stream gracefully.</p><p><span class="def">int iobase::tell()</span> returns either the current position in the target media (usually file) or, for communication channels, the number of bytes transfered from the beginning of the session.</p><p><span class="def">int iobase::seek(int newpos, ioseekmode mode = IO_BEGIN)</span> changes the media pointer (e.g. file pointer). Possible values for <span class="lang">mode</span> are: IO_BEGIN, IO_CURRENT and IO_END. This function first tries to position the stream pointer within the scope of the I/O buffer. If the new pointer is out of buffer's range, <span class="lang">seek()</span> then tries to change the physical pointer of the target media. Note that physical positioning is not supported by some stream types, e.g. by <span class="lang">ipstream</span>.</p><p><span class="def"> string iobase::get_streamname()</span> returns a string containing either a file name, an URL, or some other string describing the underlying media or object. Useful for diagnostics messages.</p><p><span class="def"> bool iobase::get/set_active(bool)</span> indicates whether the stream is active. Setting this property to <span class="lang">true</span> or <span class="lang">false</span> opens or closes the stream respectively.</p><p><span class="def"> bool iobase::get/set_cancelled(bool)</span> returns <span class="lang">true</span> if the stream was closed using <span class="lang">cancel()</span>.</p><p><span class="def"> int iobase::get/set_bufsize(int)</span> sets the buffer size for the stream. Setting this property to -1 will assign some reasonable default value, which may vary depending on the operating environment, available memory, etc. Note: text input routines require buffering (see <a href="streams.instm.html">instm</a>).</p><p><span class="def"> int iobase::get_status(int)</span> returns the current status of the stream. The value of this property can be one of the following: IO_CREATED, IO_OPENING, IO_OPENED, IO_READING, IO_WRITING, IO_EOF, IO_CLOSING, IO_CLOSED. Derivative classes may add other status codes, e.g. see <a href="inet.ipstream.html">ipstream</a>.</p><p> <span class="def"> iostatusevent iobase::get/set_onstatus(iostatusevent)</span> -- sets or returns user-defined callback function. The callback function is called whenever the status of the stream is being changed (see also <span class="lang">get_status()</span>).</p><p class="seealso">See also: <a href="streams.instm.html">instm</a>, <a href="streams.outstm.html">outstm</a>, <a href="streams.errors.html">Error handling</a></p><!-- #EndEditable --><hr size="1"><a href="../index.html" class="ns">PTypes home</a></body><!-- #EndTemplate --></html>⌨️ 快捷键说明
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