r"></A>
<H2>Optional Behavior</H2>

<P>Boost.Iostreams prvides several concepts corresponding to optional behavior that a Filter or Device might implement:</P>

<UL>
    <LI><A HREF="../concepts/blocking.html">Blocking:</A> A Device which blocks when it receives a read or write request until all requested characters are available, or until the end of a stream is reached.
    <LI><A HREF="../concepts/direct.html">Direct:</A> A Device which provides access to its controlled sequences as regions of memory rath