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<title>FBB::Sharedpos(3bobcat)</title>
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<h1 id="title">FBB::Sharedpos(3bobcat)</h1>
<h2 id="author">Shared Memory Offsets<br/>(libbobcat-dev_4.08.02-x.tar.gz)</h2>
<h2 id="date">2005-2017</h2>
<p>
<h2 >NAME</h2>FBB::Sharedpos - Shared Memory offset controller
<p>
<h2 >SYNOPSIS</h2>
<strong >#include <bobcat/sharedpos></strong><br/>
Linking option: <em >-lbobcat</em>
<p>
<h2 >DESCRIPTION</h2>
<p>
The class <strong >SharedPos</strong> is a support class for Bobcat's shared memory
handling classes. It controls the shared memory read/write ofset and ensures
that shared memory operations never exceed the shared memory's maximum offset.
<p>
The class <strong >SharedPos</strong> has several public members, but they are primarily
useful for other <em >Shared*</em> classes offered by Bobcat. There is probably
little use for a stand-alone <strong >SharedPos</strong> object.
<p>
In the descriptions of the class's member functions <em >offset</em> refers to
the read/write offset within a <strong >FBB::SharedSegment</strong>(3bobcat) object for
which <strong >SharedPos</strong> performs the offset-administration.
<p>
<h2 >NAMESPACE</h2>
<strong >FBB</strong><br/>
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace <strong >FBB</strong>.
<p>
<h2 >INHERITS FROM</h2>
-
<p>
<h2 >TYPEDEFS AND ENUMS</h2>
<p>
<h2 >CONSTRUCTORS</h2>
<p>
Default, copy and move constructors are available. The default constructor
does not yet monitor the offset of an <em >FBB::SharedSegment</em>
object. The member <em >reset</em> is used to start monitoring offsets.
<p>
<h2 >OVERLOADED OPERATORS</h2>
<ul>
<li> <strong >void operator++()</strong>:<br/>
The offset is incremented. If this member is called when the offset is
equal to the shared memory's maximum offset an <em >FBB::Exception</em> is
thrown.
<p>
<li> <strong >void operator+=(size_t len)</strong>:<br/>
The offset is incremented by <em >len</em>. If <em >offset + len</em> exceeds the
shared memory's maximum offset then the offset is set to the maximum
offset and an <em >FBB::Exception</em> is thrown.
<p>
<li> <strong >std::ostream &operator<<(std::ostream &out, SharedPos const &pos)</strong>:<br/>
Inserts information about the <strong >SharedPos</strong> object into <em >out</em>.
</ul>
<p>
Copy and move assignment operators are available.
<p>
<h2 >MEMBER FUNCTIONS</h2>
<p>
Note: the behavior of member functions returning values which refer to
information of an <em >FBB::SharedSegment</em> is undefined until the member
<em >reset</em> has been called.
<p>
<ul>
<li> <strong >bool atMaxOffset() const</strong>:<br/>
Returns <em >true</em> if offset equals the maximum offset that can be used
for the configured <em >FBB::SharedSegment</em> object.
<p>
<li> <strong >size_t blockIdx() const</strong>:<br/>
The index of the configured <em >FBB::SharedSegment</em> object's shared
segment data block to which offset refers is returned.
<p>
<li> <strong >size_t blockOffset() const</strong>:<br/>
The offset within the shared segment data block matching the member
<em >offset</em>'s return value is returned.
<p>
<li> <strong >bool eof() const</strong>:<br/>
Returns <em >true</em> if offset exceeds the maximum offset of any character
ever written to the shared memory to which the <strong >SharedPos</strong> object
interfaces. If <em >eof</em> returns <em >true</em> information may still be
<em >written</em> to the shared memory: writing is possible until the
maximum shared memory segment offset has been reached.
<p>
<li> <strong >std::streamsize eos() const</strong>:<br/>
The offset just beyond the maximum offset for the current shared
segment data block is returned. E.g., if <em >blockIdx</em> returns 5, and
the size of the shared segment data blocks equals 2000, then <em >eos</em>
returns 12000 (the first offset of segment 6).
<p>
<li> <strong >std::streamsize maxOffset() const</strong>:<br/>
The maximum possible offset that can be used for the currently
monitored <em >FBB::SharedSegment</em> is returned.
<p>
<li> <strong >std::streamsize offset() const</strong>:<br/>
The offset within the currently monitored shared memory segment is
returned.
<p>
<li> <strong >void reset(SharedSegment *sharedData)</strong>:<br/>
The <em >SharedPos</em> object is reset to monitor the offset of the
<em >FBB::SharedSegment</em> object whose address is passed as argument to
<em >reset</em>. The address must point to a <strong >sharedsegment</strong>(3bobcat)
object that must exist until the end of the <strong >SharedPos</strong>
object's lifetime or until its next <em >reset</em> call. Immediately after
calling <em >reset</em> offset is reset to 0.
<p>
<li> <strong >std::streamsize showmanyc() const</strong>:<br/>
The number of characters that can be read from the current shared
segment data block is returned. This member interrogates the number
of readable characters in the shared memory segment. This number may
change while this member is being executed. In order to receive a
stable return value, calling functions should have obtained a lock on
the <em >FBB::SharedSegment</em> data before calling this member. See also
the <strong >sharedsegment</strong>(3bobcat) man-page.
<p>
<li> <strong >std::ios::pos_type seek(std::ios::off_type offset,
std::ios::seekdir origin = std::ios::beg)</strong>:<br/>
The monitored offset is changed to this member's <em >offset</em> argument,
relative to <em >origin</em>. Seeking beyond <em >eof</em> is OK. However, -1 is
returned when seeking beyond <em >maxOffset</em> or seeking before the
shared segment's offset 0.
</ul>
<p>
<h2 >EXAMPLE</h2>
See the <strong >sharedstream</strong>(3bobcat) man page.
<p>
<h2 >FILES</h2>
<em >bobcat/sharedpos</em> - defines the class interface
<p>
<h2 >SEE ALSO</h2>
<strong >bobcat</strong>(7),
<strong >isharedstream</strong>(3bobcat),
<strong >osharedstream</strong>(3bobcat),
<strong >sharedblock</strong>(3bobcat),
<strong >sharedcondition</strong>(3bobcat),
<strong >sharedmemory</strong>(3bobcat),
<strong >sharedmutex</strong>(3bobcat),
<strong >sharedreadme</strong>(7bobcat),
<strong >sharedsegment</strong>(3bobcat),
<strong >sharedstream</strong>(3bobcat),
<strong >sharedstreambuf</strong>(3bobcat)
<p>
<h2 >BUGS</h2>
None Reported.
<p>
<h2 >DISTRIBUTION FILES</h2>
<ul>
<li> <em >bobcat_4.08.02-x.dsc</em>: detached signature;
<li> <em >bobcat_4.08.02-x.tar.gz</em>: source archive;
<li> <em >bobcat_4.08.02-x_i386.changes</em>: change log;
<li> <em >libbobcat1_4.08.02-x_*.deb</em>: debian package holding the
libraries;
<li> <em >libbobcat1-dev_4.08.02-x_*.deb</em>: debian package holding the
libraries, headers and manual pages;
<li> <em >http://sourceforge.net/projects/bobcat</em>: public archive location;
</ul>
<p>
<h2 >BOBCAT</h2>
Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
<p>
<h2 >COPYRIGHT</h2>
This is free software, distributed under the terms of the
GNU General Public License (GPL).
<p>
<h2 >AUTHOR</h2>
Frank B. Brokken (<strong >f.b.brokken@rug.nl</strong>).
<p>
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