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1 <?xml version="1.0" encoding="utf-8"?> |
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2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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3 <!-- This component and the accompanying materials are made available under the terms of the License |
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4 "Eclipse Public License v1.0" which accompanies this distribution, |
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5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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6 <!-- Initial Contributors: |
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7 Nokia Corporation - initial contribution. |
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8 Contributors: |
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9 --> |
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10 <!DOCTYPE concept |
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11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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12 <concept id="GUID-2DDAAD1C-D9EB-5741-B6AE-2383646E0EDB" xml:lang="en"><title>Pointer |
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13 descriptors</title><shortdesc>Describes non-modifiable pointer descriptors and modifiable pointer |
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14 descriptors.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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15 <p>A pointer descriptor represents data which can live in ROM or RAM and this |
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16 location is separate from the pointer descriptor object itself. </p> |
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17 <p>A pointer descriptor is an instance of a class that encapsulates a pointer |
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18 to the location of the data. </p> |
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19 <p>A pointer descriptor comes in two forms: </p> |
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20 <ul> |
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21 <li id="GUID-A836665F-9AB7-5364-891E-6297D68B291D"><p>a non-modifiable pointer |
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22 descriptor. </p> </li> |
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23 <li id="GUID-C46BB0C8-08ED-5835-9516-D164383D1313"><p>a modifiable pointer |
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24 descriptor. </p> </li> |
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25 </ul> |
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26 <section id="GUID-DE207726-9C75-4DD9-964A-6B7B16226C4A"><title>Non-modifiable pointer descriptor</title> <p>The data represented |
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27 by a non-modifiable pointer descriptor can be accessed, but not changed, through |
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28 this descriptor. </p> <p>Data is accessed through functions provided by the |
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29 base class. </p> <p>A non-modifiable pointer descriptor is supplied in two |
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30 variants: </p> <ul> |
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31 <li id="GUID-CF4D06B5-B5EB-5C4D-BA87-B990053CD15D"><p>the 16 bit variant, |
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32 a <codeph>TPtrC16</codeph>, for representing Unicode strings. </p> </li> |
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33 <li id="GUID-A1005460-2D2A-5DB4-9414-2747056A7DBC"><p>the 8 bit variant, a <codeph>TPtrC8</codeph>, |
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34 for representing non-Unicode strings and binary data. </p> </li> |
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35 </ul> <p>There is also a build independent type, <codeph>TPtrC</codeph>. This |
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36 is the type which is most commonly used in program code; the appropriate variant |
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37 is selected at build time. </p> <p>An explicit 8 bit variant is chosen for |
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38 binary data. The explicit 16 bit variant is rarely used. </p> <p>The base |
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39 class, <codeph>TDesC</codeph>, contains a data member which holds the length |
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40 of the data. The following drawing shows the layout of a <codeph>TPtrC</codeph> object |
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41 for a string of five characters representing the English word "Hello". </p> <fig id="GUID-D3F0600A-D575-5309-8182-CFA98D184E29"> |
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42 <image href="GUID-37D2EFAE-FB55-5015-90CE-1361144C411E_d0e224612_href.png" placement="inline"/> |
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43 <p>Non-modifiable pointer descriptor</p> |
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44 </fig> </section> |
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45 <section id="GUID-33072A44-C95A-4688-AB85-019EFDC4F1B2"><title>Modifiable pointer descriptor</title> <p>The data represented |
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46 by a modifiable pointer descriptor can be both accessed and changed through |
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47 this descriptor. </p> <p>The length of the data can vary between zero and |
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48 the maximum length. The maximum length of the descriptor is set by the constructor. |
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49 When the length of the data is less than the maximum, a portion of the data |
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50 area represented by the descriptor is unused. </p> <p>Data is accessed and |
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51 modified through functions provided by the base classes. </p> <p>A modifiable |
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52 pointer descriptor is supplied in two variants: </p> <ul> |
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53 <li id="GUID-2DD694B8-8408-58F8-BE98-1D031666DEC5"><p>the 16 bit variant, |
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54 a <codeph>TPtr16</codeph>, for representing Unicode strings. </p> </li> |
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55 <li id="GUID-5D1EB254-6B9D-576C-9631-3461AC8FFD32"><p>the 8 bit variant, a <codeph>TPtr8</codeph>, |
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56 for representing non-Unicode strings and binary data. </p> </li> |
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57 </ul> <p>There is also a build independent type, <codeph>TPtr</codeph>. This |
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58 is the type which is most commonly used in program code; the appropriate variant |
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59 is selected at build time. </p> <p>An explicit 8 bit variant is chosen for |
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60 binary data. The explicit 16 bit variant is rarely used. </p> <p>The base |
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61 class <codeph>TDesC</codeph>, contains a data member that holds the length |
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62 of the data. The base class <codeph>TDes</codeph>, contains a data member |
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63 that holds the maximum length of the data. The following drawing shows the |
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64 layout of a <codeph>TPtr</codeph> object for a string of five characters representing |
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65 the English word "Hello". The maximum length to be represented by the descriptor |
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66 is 12. </p> <fig id="GUID-B6213E7F-AE00-5854-BBB7-C82BE71CB495"> |
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67 <image href="GUID-8983A095-3F5A-5262-8920-8A13ADD045DC_d0e224677_href.png" placement="inline"/> |
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68 <p>Modifiable pointer descriptor</p> |
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69 </fig> </section> |
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70 </conbody></concept> |