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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-C642BA79-0E9B-5C62-9DC7-C64759830CD4" xml:lang="en"><title>Dynamic

buffers versus descriptors, arrays and heap cells</title><shortdesc>Explains the difference between various types of buffers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The essential difference between dynamic buffers and more straightforward

means of storing binary data is that C arrays and descriptors provide essentially

non-extensible buffers. Any attempt to write beyond the end of a C array results

in undefined (and usually disastrous) consequences. Any attempt to write beyond

the end of a descriptor results in a panic.</p>

<p>Heap cells may be extended, but not without limit; it may be impossible

to extend a heap cell further, because the heap is exhausted, or too fragmented

to permit the extension. In addition, if heap cell re-allocation results in

movement of the cell, re-allocation can be unduly expensive. If re-allocation

is undesirable, then a buffer could be extended by allocating a new segment

in a new allocation cell. Segmented buffers have this behaviour: flat buffers

use re-allocation alone.</p>

</conbody></concept>