Symbian3/SDK/Source/GUID-2DDAAD1C-D9EB-5741-B6AE-2383646E0EDB.dita
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     1 <?xml version="1.0" encoding="utf-8"?>
       
     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
       
     3 <!-- This component and the accompanying materials are made available under the terms of the License 
       
     4 "Eclipse Public License v1.0" which accompanies this distribution, 
       
     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
       
     6 <!-- Initial Contributors:
       
     7     Nokia Corporation - initial contribution.
       
     8 Contributors: 
       
     9 -->
       
    10 <!DOCTYPE concept
       
    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
       
    12 <concept id="GUID-2DDAAD1C-D9EB-5741-B6AE-2383646E0EDB" xml:lang="en"><title>Pointer
       
    13 descriptors</title><shortdesc>Describes non-modifiable pointer descriptors and modifiable pointer
       
    14 descriptors.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
       
    15 <p>A pointer descriptor represents data which can live in ROM or RAM and this
       
    16 location is separate from the pointer descriptor object itself. </p>
       
    17 <p>A pointer descriptor is an instance of a class that encapsulates a pointer
       
    18 to the location of the data. </p>
       
    19 <p>A pointer descriptor comes in two forms: </p>
       
    20 <ul>
       
    21 <li id="GUID-A836665F-9AB7-5364-891E-6297D68B291D"><p>a non-modifiable pointer
       
    22 descriptor. </p> </li>
       
    23 <li id="GUID-C46BB0C8-08ED-5835-9516-D164383D1313"><p>a modifiable pointer
       
    24 descriptor. </p> </li>
       
    25 </ul>
       
    26 <section id="GUID-DE207726-9C75-4DD9-964A-6B7B16226C4A"><title>Non-modifiable pointer descriptor</title> <p>The data represented
       
    27 by a non-modifiable pointer descriptor can be accessed, but not changed, through
       
    28 this descriptor. </p> <p>Data is accessed through functions provided by the
       
    29 base class. </p> <p>A non-modifiable pointer descriptor is supplied in two
       
    30 variants: </p> <ul>
       
    31 <li id="GUID-CF4D06B5-B5EB-5C4D-BA87-B990053CD15D"><p>the 16 bit variant,
       
    32 a <codeph>TPtrC16</codeph>, for representing Unicode strings. </p> </li>
       
    33 <li id="GUID-A1005460-2D2A-5DB4-9414-2747056A7DBC"><p>the 8 bit variant, a <codeph>TPtrC8</codeph>,
       
    34 for representing non-Unicode strings and binary data. </p> </li>
       
    35 </ul> <p>There is also a build independent type, <codeph>TPtrC</codeph>. This
       
    36 is the type which is most commonly used in program code; the appropriate variant
       
    37 is selected at build time. </p> <p>An explicit 8 bit variant is chosen for
       
    38 binary data. The explicit 16 bit variant is rarely used. </p> <p>The base
       
    39 class, <codeph>TDesC</codeph>, contains a data member which holds the length
       
    40 of the data. The following drawing shows the layout of a <codeph>TPtrC</codeph> object
       
    41 for a string of five characters representing the English word "Hello". </p> <fig id="GUID-D3F0600A-D575-5309-8182-CFA98D184E29">
       
    42 <image href="GUID-37D2EFAE-FB55-5015-90CE-1361144C411E_d0e195991_href.png" placement="inline"/>
       
    43 <p>Non-modifiable pointer descriptor</p>
       
    44 </fig> </section>
       
    45 <section id="GUID-33072A44-C95A-4688-AB85-019EFDC4F1B2"><title>Modifiable pointer descriptor</title> <p>The data represented
       
    46 by a modifiable pointer descriptor can be both accessed and changed through
       
    47 this descriptor. </p> <p>The length of the data can vary between zero and
       
    48 the maximum length. The maximum length of the descriptor is set by the constructor.
       
    49 When the length of the data is less than the maximum, a portion of the data
       
    50 area represented by the descriptor is unused. </p> <p>Data is accessed and
       
    51 modified through functions provided by the base classes. </p> <p>A modifiable
       
    52 pointer descriptor is supplied in two variants: </p> <ul>
       
    53 <li id="GUID-2DD694B8-8408-58F8-BE98-1D031666DEC5"><p>the 16 bit variant,
       
    54 a <codeph>TPtr16</codeph>, for representing Unicode strings. </p> </li>
       
    55 <li id="GUID-5D1EB254-6B9D-576C-9631-3461AC8FFD32"><p>the 8 bit variant, a <codeph>TPtr8</codeph>,
       
    56 for representing non-Unicode strings and binary data. </p> </li>
       
    57 </ul> <p>There is also a build independent type, <codeph>TPtr</codeph>. This
       
    58 is the type which is most commonly used in program code; the appropriate variant
       
    59 is selected at build time. </p> <p>An explicit 8 bit variant is chosen for
       
    60 binary data. The explicit 16 bit variant is rarely used. </p> <p>The base
       
    61 class <codeph>TDesC</codeph>, contains a data member that holds the length
       
    62 of the data. The base class <codeph>TDes</codeph>, contains a data member
       
    63 that holds the maximum length of the data. The following drawing shows the
       
    64 layout of a <codeph>TPtr</codeph> object for a string of five characters representing
       
    65 the English word "Hello". The maximum length to be represented by the descriptor
       
    66 is 12. </p> <fig id="GUID-B6213E7F-AE00-5854-BBB7-C82BE71CB495">
       
    67 <image href="GUID-8983A095-3F5A-5262-8920-8A13ADD045DC_d0e196056_href.png" placement="inline"/>
       
    68 <p>Modifiable pointer descriptor</p>
       
    69 </fig> </section>
       
    70 </conbody></concept>