<?xml version="1.0" encoding="utf-8"?>+
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->+
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<!-- This component and the accompanying materials are made available under the terms of the License +
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"Eclipse Public License v1.0" which accompanies this distribution, +
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->+
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<!-- Initial Contributors:+
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    Nokia Corporation - initial contribution.+
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Contributors: +
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-->+
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<!DOCTYPE concept+
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">+
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<concept id="GUID-8E363123-A85E-521C-BC10-96C59130E45C" xml:lang="en"><title>How+
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to walk the heap</title><shortdesc>The <codeph>THeapWalk</codeph> class provides behaviour for walking+
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the heap. This class is pure virtual and developers must provide a derived+
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class in order to use it.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>+
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<p>A heap can be checked to make sure that its allocated and free cells are+
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in a consistent state and that the heap is not corrupt.</p>+
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<p>The <codeph>THeapWalk</codeph> class provides the behaviour for doing this.+
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This class is pure virtual and developers must provide a derived class in+
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order to use it.</p>+
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<p>Simply construct a <codeph>THeapWalk</codeph> derived object, passing a+
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reference to the heap which is to be checked in its constructor. Walking the+
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heap is initiated by calling <codeph>Walk()</codeph>. This function follows+
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the list of allocated and free cells in the heap. The function calls the virtual+
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function <codeph>Info()</codeph> for every good cell it finds, passing the+
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cell's address and length.</p>+
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<p><codeph>Info()</codeph> is a pure virtual function and a derived class+
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must provide an implementation for it.</p>+
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<p><codeph>Walk()</codeph> terminates when it has successfully followed the+
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entire list of free and allocated cells or until it finds the first bad cell.</p>+
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<p>As a minimum, a class derived from <codeph>THeapWalk</codeph> might be:</p>+
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<codeblock id="GUID-A3AC2314-4C1E-5F1F-9BCB-694893AB47FB" xml:space="preserve">class TMyClass : public THeapWalk+
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    {</codeblock>+
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<codeblock id="GUID-C45FDA92-5BEE-57A3-BB1B-F4AB203EC0EC" xml:space="preserve">public :+
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    TMyClass(RHeap&amp; aHeap);+
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    void Info(TCellType aType,TAny *aBase,TInt aLength);+
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    }</codeblock>+
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<p>where the constructor would be implemented as:</p>+
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<codeblock id="GUID-F7B66153-EAFE-570C-997F-42BDBB05DE01" xml:space="preserve">TMyClass::TMyClass(RHeap&amp; aHeap)+
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    : THeapWalk(aHeap)+
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    {}</codeblock>+
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<p>Typically, the <codeph>Info()</codeph> function might consist of a switch+
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statement based on the value of <codeph>aType</codeph>:</p>+
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<codeblock id="GUID-379F76EF-8FC0-5085-BB05-373E2B64508C" xml:space="preserve">TMyClass::Info(TCellType aType,TAny *aBase,TInt aLength)+
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    {+
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    switch(aType)+
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        {+
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    case EGoodAllocatedCell:+
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        ...+
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        break;+
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    case EGoodFreeCell:+
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        ...+
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        break;+
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    case EBadFreeCellAddress:+
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        ...+
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        break;+
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    default:+
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        ...+
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        }+
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    }</codeblock>+
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</conbody></concept>+
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