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    10 <!DOCTYPE concept

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

    12 <concept id="GUID-82862A69-5E86-5924-BFF0-F7655FCBFAF0" xml:lang="en"><title>Contiguousness</title><shortdesc>Description of contiguous data in flat and segmented buffers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    13 <p>In flat buffers, all data is contiguous. The <codeph>Ptr()</codeph> function

    14 always returns a pointer descriptor from the buffer position specified to

    15 the end of the data, and the <codeph>BackPtr()</codeph> function always returns

    16 a pointer descriptor from the beginning of the buffer to the buffer position

    17 specified.</p>

    18 <p>In segmented buffers, data is contained in segments and the maximum length

    19 of contiguous data is the granularity of the buffer. The extent of contiguous

    20 data contained in a segment may vary between a single byte, and the granularity,

    21 if the insertion and deletion pattern is arbitrary.</p>

    22 <p>However, the following guarantee is made: if the number of bytes inserted

    23 or deleted in <i>all</i> insertion and deletion operations is a multiple of

    24 some number <i>n</i>, and the granularity is also a multiple of this number <i>n</i>,

    25 then all data extents will be a multiple of <i>n</i> in length. This implies

    26 that the <codeph>Ptr()</codeph> function, given a buffer position which is

    27 a multiple of <i>n</i>, will always return a pointer descriptor referring

    28 to at least <i>n</i> bytes.</p>

    29 <p>This property of segmented descriptors is exploited by the <codeph>CArrayFixBase</codeph>, <codeph>CArrayVarBase</codeph> and <codeph>CArrayPakBase</codeph> derived array classes. In these classes, all insertion or deletion operations

    30 are always done in terms of the (fixed) length of data stored in the buffer.

    31 Therefore, the data for an individual array element is always contiguous.</p>

    32 </conbody><related-links>

    33 <link>

    34 <desc><xref href="GUID-2F64B579-73D3-548A-9104-16483AF77BCB.dita">Dynamic Arrays</xref></desc>

    35 </link>

    36 </related-links></concept>