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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-6163197B-7983-5FB7-9B92-02E490A900FB" xml:lang="en"><title>How to |
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13 construct a header</title><shortdesc>This document describes how to create a header for a doubly linked |
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14 list.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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15 <p>In order to construct a header, two important pieces of information are |
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16 needed:</p> |
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17 <ul> |
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18 <li id="GUID-2E721D77-E010-5211-BABE-94578AECEEE4"><p>the <i>type</i> of object |
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19 which forms the elements.</p> </li> |
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20 <li id="GUID-71FC8FBF-803F-55BC-AC52-D672B1DA36BA"><p>the <i>offset</i> of |
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21 the link object from the start of the element.</p> </li> |
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22 </ul> |
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23 <p>To create a header for a doubly linked list of <codeph>CMyClass</codeph> elements, |
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24 defined as:</p> |
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25 <codeblock id="GUID-D995F2F7-6A38-5EE3-9210-1302E1662759" xml:space="preserve">class CMyClass : public CBase |
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26 { |
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27 ... |
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28 TDblQueLink iDlink; |
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29 ... |
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30 };</codeblock> |
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31 <p>construct a <codeph>TDblQue</codeph> as follows:</p> |
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32 <codeblock id="GUID-D13C33D2-EE7E-5915-92E2-F3EC5C772B4D" xml:space="preserve">TDblQue<CMyClass> queHeader(_FOFF(CMyClass,iDlink));</codeblock> |
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33 <p>The <codeph>TDblQue</codeph> class takes a class template parameter which |
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34 defines the type of object which is to form an element of the list. In this |
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35 example, objects of type <codeph>CMyClass</codeph> form the elements of the |
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36 list.</p> |
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37 <p>The <codeph>_FOFF</codeph> macro (i.e. the "field offset" macro) calculates |
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38 the offset of the component link object within the element. In this example, |
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39 the required value is the offset of the <codeph>iDlink</codeph> data member |
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40 from the start of <codeph>CMyClass</codeph>. </p> |
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41 <fig id="GUID-9C102C34-EFFA-530A-AA1E-C6AE08FDFA37"> |
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42 <title/> |
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43 <image href="GUID-29E7942D-A00D-5771-9782-59260965C687_d0e189052_href.png" placement="inline"/> |
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44 </fig> |
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45 </conbody></concept> |