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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<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();
large tellx();
int tell();
large seekx(large newpos, ioseekmode mode = IO_BEGIN);
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">large iobase::tellx()</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::tell()</span> left for compatibility; returns a 32-bit file offset or raises an exception if the value doesn't fit the <span class="lang">int</span> type.</p>
<p><span class="def">large iobase::seekx(large 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">seekx()</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">int iobase::seek(int newpos, ioseekmode mode = IO_BEGIN)</span> left for compatibility; tries to seek in 32-bit mode and return a 32-bit file offset. Raises an exception if the return value doesn't fir the <span class="lang">int</span> type.</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 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>
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