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<title>FBB::OSharedStream(3bobcat)</title>
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<h1 id="title">FBB::OSharedStream(3bobcat)</h1>
<h2 id="author">std::ostream on shared memory<br/>(libbobcat-dev_4.08.02-x.tar.gz)</h2>
<h2 id="date">2005-2017</h2>
<p>
<h2 >NAME</h2>FBB::OSharedStream - std::ostream operations on shared memory
<p>
<h2 >SYNOPSIS</h2>
<strong >#include <bobcat/osharedstream></strong><br/>
Linking option: <em >-lpthread -lbobcat</em>
<p>
<h2 >DESCRIPTION</h2>
<p>
This class offers the features of the <strong >std::ostream</strong> class, operating on
shared memory.
<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>
<strong >FBB::OSharedStreambuf</strong> (private inheritance),<br/>
<strong >std::ostream</strong>,<br/>
<strong >FBB::SharedEnum__</strong> (cf. <strong >sharedmemory(3bobcat)</strong> for a description of
this last base class).
<p>
<h2 >SIZEUNIT ENUMERATION</h2>
<p>
The <strong >enum SizeUnit</strong> defines the following symbolic constants:
<ul>
<li> <strong >kB</strong>, representing 1024 (2**10) bytes of memory;
<li> <strong >MB</strong>, representing 1048576 (2**20 bytes of memory;
<li> <strong >GB</strong>, representing 1073741824 (2**30) bytes of memory
)
<p>
<h2 >CONSTRUCTORS</h2>
<ul>
<li> <strong >OSharedStream()</strong>:<br/>
The default constructor defines a stub a <strong >OSharedStream</strong> object that
cannot immediately be used to access shared memory. To use it, its
member <em >open</em> must first be called.
<p>
<li> <strong >OSharedStream(size_t maxSize, SizeUnit sizeUnit,
std::ios::openmode openMode = std::ios::out,
size_t access = 0600)</strong>:<br/>
This constructor creates an <em >std::ostream</em> that interfaces to a
shared memory segment having a capacity of at least <em >maxSize *
sizeUnit</em> bytes. By default, the shared memory segment is opened for
writing. The shared memory's access rights are defined by the
<em >access</em> parameter, using the well-known (<strong >chmod</strong>(1)) way to
define the access rights for the owner, the group and others, using
octal digits. If construction succeeds the shared memory is ready for
use. If construction fails, an <em >FBB::Exception</em> is thrown.
<p>
<li> <strong >OSharedStreambuf(int id, std::ios::openmode openMode = std::ios::out |
std::ios::in)</strong>:<br/>
This constructor creates an <em >std::istream</em> that connects to a shared
memory segment having ID <em >id</em>. If construction succeeds the shared
memory is ready for use. If construction fails (e.g., no shared memory
segment having ID <em >id</em> exists), an <em >FBB::Exception</em> is thrown.
</ul>
Copy and move constructors are not available.
<p>
<h2 >OVERLOADED OPERATORS</h2>
<p>
The overloaded move and copy assignment operators are not available.
<p>
<h2 >MEMBER FUNCTIONS</h2>
<p>
All members of <em >std::istream</em> and <em >std::ostream</em> and the <em >enum</em>
values <em >kB, MB</em>, and <em >GB</em>, defined by <em >FBB::OSharedEnum__</em> are available.
<p>
<ul>
<li> <strong >FBB::SharedCondition attachSharedCondition(std::ios::off_type offset,
std::ios::seekdir origin)</strong>:<br/>
Returns an <strong >FBB::SharedCondition</strong>(3) object, interfacing to a shared
condition variable located at offset <em >offset</em> (relative to
<em >origin</em>) in the <em >SharedMemory</em> object to which the
<strong >OSharedStream</strong> object interfaces. This member does not alter the
value returned by the stream's <em >tellp</em> member.
<p>
An <em >FBB::Exception</em> is thrown if the <em >FBB::SharedCondition</em> object
could not be constructed.
<p>
<li> <strong >FBB::SharedCondition createSharedCondition()</strong>:<br/>
Returns an <strong >FBB::SharedCondition</strong>(3) object, interfacing to a newly
created shared condition variable which is created at the current
offset of the <em >SharedMemory</em> object to which the <strong >OSharedStream</strong>
object interfaces (or at the first offset of the next physical shared
memory data block, cf. <strong >sharedcondition</strong>(3bobcat))</ul>. Creating a
<em >SharedCondition</em> object does not alter the value returned by the
stream's <em >tellp</em> member.
<p>
An <em >FBB::Exception</em> is thrown if the <em >FBB::SharedCondition</em> object
could not be constructed.
<p>
<li> <strong >int id() const</strong>:<br/>
The ID of the shared memory segment is returned.
<p>
<li> <strong >void kill()</strong>:<br/>
Without locking the shared memory first, all shared memory is returned
to the operating system. The <strong >FBB::OSharedStream</strong> object is unusable
after returning from <em >kill</em>. Other processes that were using the
shared memory can continue to do so.
<p>
<li> <strong >void memInfo(std::ostream &out, char const *end = "\n")</strong>:<br/>
Information about the <em >OSharedMemory</em> object is inserted into the
provide <em >ostream</em> object. The IDs of the shared segments, their
sizes, the maximum number of shared memory segments, the number of
bytes that can be read from the shared memory, and its actual storage
capacity, etc., are displayed. Following the information about the
shaed memory, <em >end</em> is inserted into <em >out</em>.
<p>
<li> <strong >void open(size_t maxSize, SizeUnit sizeUnit,
std::ios::openmode openMode = std::ios::out,
size_t access = 0600)</strong>:<br/>
This member creates a shared memory segment having a capacity of at
least <em >maxSize * sizeUnit</em> bytes, and connects the shared memory
segment to the <strong >FBB::OSharedStream</strong>. A matching <em >close</em> member
does not exist and is not required. By default, the shared memory
segment is opened for reading. Different from the open modes used for
file streams, creating a shared memory stream with open modes
<em >ios::in</em> is OK. In this case the shared memory segment is created
and once information has been written to the shared memory by another
process it can be read. The shared memory's access rights are defined
by the <em >access</em> parameter, using the well-known (<strong >chmod</strong>(1)) way
to define the access rights for the owner, the group and others, using
octal digits. If opening succeeds the shared memory is ready for
use. If opening fails, an <em >FBB::Exception</em> is thrown.
<p>
<li> <strong >void open(int id, std::ios::openmode openMode = std::ios::in |
std::ios::out)</strong>:<br/>
This member connects the <strong >FBB::OSharedStream</strong> object to a shared
memory segment having ID <em >id</em>. A matching <em >close</em> member does
not exist and is not required. If opening succeeds the shared
memory is ready for use. If opening fails (e.g., no shared memory
segment having ID <em >id</em> exists), an <em >FBB::Exception</em> is
thrown.
<p>
<li> <strong >void remove()</strong>:<br/>
The shared memory is first locked. Next, all shared memory is returned
to the operating system. The <strong >FBB::OSharedStream</strong> object is unusable
after returning from <em >remove</em>. Other processes that were using the
shared memory can continue to do so.
<p>
<li> <strong >bool truncate(std::streamsize offset)</strong>:<br/>
If <em >offset</em> is not exceeding the value returned by <em >seekp(0,
std::ios::end)</em> this latter value is changed to <em >offset</em> and
<em >true</em> is returned. Otherwise <em >false</em> is returned, and the value
returned by <em >seekp</em> is not altered. If the value returned by
<em >tellp</em> exceeded <em >offset</em>, <em >tellp</em>'s return value is reduced to
<em >offset</em> as well.
</ul>
<p>
<h2 >EXAMPLE</h2>
See the <strong >sharedstream</strong>(3bobcat) man page.
<p>
<h2 >FILES</h2>
<em >bobcat/osharedstream</em> - defines the class interface
<p>
<h2 >SEE ALSO</h2>
<strong >bobcat</strong>(7), <strong >chmod</strong>(1),
<strong >isharedstream</strong>(3bobcat),
<strong >sharedblock</strong>(3bobcat),
<strong >sharedcondition</strong>(3bobcat),
<strong >sharedmemory</strong>(3bobcat)
<strong >sharedmutex</strong>(3bobcat),
<strong >sharedpos</strong>(3bobcat),
<strong >sharedreadme</strong>(7bobcat),
<strong >sharedsegment</strong>(3bobcat),
<strong >sharedstream</strong>(3bobcat),
<strong >sharedstreambuf</strong>(3bobcat)
<p>
<h2 >BUGS</h2>
Note that by default exceptions thrown from within a <strong >std::stream</strong>
object are caught by the stream object, setting its <em >ios::failbit</em> flag. To
allow exceptions to leave a stream object, its <em >exceptions</em> member can be
called, e.g., using:
<pre>
myStream.exceptions(ios::failbit | ios::badbit | ios::eofbit);
</pre>
<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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