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<concept id="GUID-E161AB84-1B24-53AF-B313-D68CF9F8EE60" xml:lang="en"><title>Pointers

to the start and end of contiguous regions</title><shortdesc>The <codeph>Back()</codeph> and <codeph>End()</codeph> functions

point to locations in memory for flat and segmented arrays.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>For those arrays of same length elements which are derived from <codeph>CArrayFix&lt;class T&gt;</codeph>,

the elements are contained within an array buffer which can be implemented

as a flat buffer or as a segmented buffer. A flat buffer is implemented as

a single contiguous region of memory while a segmented buffer is implemented

as a set of separate but linked regions of memory </p>

<p>Given the position of an element within an array, it can be useful to fetch

a pointer to the first byte following the end of the contiguous region of

memory containing that element (the <i>end</i> pointer). Similarly, it can

be useful to fetch a pointer to the <i>beginning</i> of a contiguous region

of memory (the <i>back</i> pointer).</p>

<section id="GUID-DB6D5E2F-CFEE-47EC-B38D-9D0DC13B994D"><title>Array of same length elements</title> <p>An array of same

length elements uses the <codeph>End()</codeph> function to fetch the end

pointer and the <codeph>Back()</codeph> function to fetch the back pointer.

The implementation of these two functions differs between a fixed flat array

and a fixed segmented array.</p> </section>

<section id="GUID-48756A91-9B8F-4BA8-A0CF-52970F8B41CC"><title>Flat array</title> <p>For a flat array — i.e. an array whose

buffer is implemented using a flat buffer — the end pointer simply points

to the first byte following the single region of memory containing the array

buffer. The back pointer simply points to the first byte of the single region

of memory (as illustrated below); <codeph>End()</codeph> always returns a

pointer to the first byte following the end of the buffer, while <codeph>Back()</codeph> always

returns a pointer to the beginning of the buffer.</p> <fig id="GUID-D4084F4C-B928-5779-A58F-CB495A74EE68">

<title>End() and Back() in fixed flat arrays</title>

<image href="GUID-81A5784D-A0C6-5108-9E7B-5D39C6743B1A_d0e216847_href.png" placement="inline"/>

</fig> </section>

<section id="GUID-27F85346-3B08-4E06-A80D-A5B708105659"><title>Segmented array</title> <p>For a segmented array, the situation

is different (as illustrated below). Looking at the segment containing elements <codeph>n</codeph> and <codeph>n+1</codeph>, <codeph>End()</codeph> returns a pointer to the first byte following the end of that segment. In

fact, <codeph>End()</codeph> returns the same pointer value for all elements

in that segment. <codeph>Back()</codeph> returns a pointer to the beginning

of that segment for element <codeph>n+1</codeph> and for all <i>subsequent</i> elements

in that segment. However, for the <i>first</i> element in that segment, <codeph>Back()</codeph> returns

a pointer to the beginning of the <i>previous</i> segment. For the very first

element in the array, <codeph>Back()</codeph> returns a pointer with a NULL

value.</p> <fig id="GUID-90C05AF9-9048-557E-95DD-49A19F856EF0">

<title>End() and Back() in fixed segmented arrays</title>

<image href="GUID-C0CFFE13-579C-5A93-9B63-DC2DCF98EC61_d0e216896_href.png" placement="inline"/>

</fig> </section>

<section id="GUID-165D9F3E-3948-4DC0-9632-FF70480C495C"><title>See also</title> <p><xref href="GUID-112AAFA5-B4C9-5B62-A106-FB5097C13A0E.dita">Dynamic

Buffers Guide</xref>.</p> </section>

</conbody></concept>