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<concept id="GUID-8E363123-A85E-521C-BC10-96C59130E45C" xml:lang="en"><title>How

to walk the heap</title><shortdesc>The <codeph>THeapWalk</codeph> class provides behaviour for walking

the heap. This class is pure virtual and developers must provide a derived

class in order to use it.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>A heap can be checked to make sure that its allocated and free cells are

in a consistent state and that the heap is not corrupt.</p>

<p>The <codeph>THeapWalk</codeph> class provides the behaviour for doing this.

This class is pure virtual and developers must provide a derived class in

order to use it.</p>

<p>Simply construct a <codeph>THeapWalk</codeph> derived object, passing a

reference to the heap which is to be checked in its constructor. Walking the

heap is initiated by calling <codeph>Walk()</codeph>. This function follows

the list of allocated and free cells in the heap. The function calls the virtual

function <codeph>Info()</codeph> for every good cell it finds, passing the

cell's address and length.</p>

<p><codeph>Info()</codeph> is a pure virtual function and a derived class

must provide an implementation for it.</p>

<p><codeph>Walk()</codeph> terminates when it has successfully followed the

entire list of free and allocated cells or until it finds the first bad cell.</p>

<p>As a minimum, a class derived from <codeph>THeapWalk</codeph> might be:</p>

<codeblock id="GUID-A3AC2314-4C1E-5F1F-9BCB-694893AB47FB" xml:space="preserve">class TMyClass : public THeapWalk

    {</codeblock>

<codeblock id="GUID-C45FDA92-5BEE-57A3-BB1B-F4AB203EC0EC" xml:space="preserve">public :

    TMyClass(RHeap& aHeap);

    void Info(TCellType aType,TAny *aBase,TInt aLength);

    }</codeblock>

<p>where the constructor would be implemented as:</p>

<codeblock id="GUID-F7B66153-EAFE-570C-997F-42BDBB05DE01" xml:space="preserve">TMyClass::TMyClass(RHeap&amp; aHeap)

    : THeapWalk(aHeap)

    {}</codeblock>

<p>Typically, the <codeph>Info()</codeph> function might consist of a switch

statement based on the value of <codeph>aType</codeph>:</p>

<codeblock id="GUID-379F76EF-8FC0-5085-BB05-373E2B64508C" xml:space="preserve">TMyClass::Info(TCellType aType,TAny *aBase,TInt aLength)

    {

    switch(aType)

        {

    case EGoodAllocatedCell:

        ...

        break;

    case EGoodFreeCell:

        ...

        break;

    case EBadFreeCellAddress:

        ...

        break;

    default:

        ...

        }

    }</codeblock>

</conbody></concept>