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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-59FFCA8F-5F2C-55F9-B864-AFA1CC18722D" xml:lang="en"><title>Buffer
position</title><shortdesc>How to use buffer position with other functions.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>All operations are specified in terms of a <i>buffer position</i>, which
is an integer whose valid range is zero to the size of the buffer. The buffer
position is a byte offset into the buffer’s data.</p>
<p>The <codeph>InsertL()</codeph> and <codeph>DeleteL()</codeph> functions
cause data after the inserted or deleted region to be shuffled up or down
the buffer as appropriate; also, <codeph>InsertL()</codeph> even at the end
of a flat buffer may cause re-allocation which may move the cell’s position
in memory. Because of this, the memory address corresponding to a buffer position
may change. Therefore, any pointer references to data in a buffer — including
pointers inside descriptors — must be updated (or discarded) after the buffer
is updated in any way.</p>
<p>It is recommended that all references to data in buffers be maintained
in terms of the buffer position. When data is inserted or deleted, buffer
positions after the beginning of the insertion or deletion position must be
adjusted (or, in the case of positions inside a deleted region, discarded).
The amount of the adjustment is the length of the inserted or deleted data.</p>
<p>Pointers cannot be maintained as simply as buffer positions. In the case
of flat buffers, re-allocation may cause the entire buffer’s address to change.
In the case of segmented buffers, data is discontiguous and the segmentation
algorithm is not straightforward. Therefore, it is recommended that pointer
references be <i>discarded</i> after any update, and that adjustments to pointer
references always use the <codeph>CBufBase</codeph> programming interface,
rather than user program calculations.</p>
</conbody></concept>