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<concept id="GUID-4F8B0675-AC8D-529A-903D-DA31C8236A98" xml:lang="en"><title>Using

TArray&lt;class T&gt;</title><shortdesc>This document covers important issues in using TArray</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-658749FD-5BE8-4233-B107-DA466FB662CF"><title>Using TArray to avoid the need for overloaded variants</title> <p>The

use of a <codeph>TArray</codeph> object can avoid the need for the member

function of an end-user class to have overloaded variants to handle all possible

types of arrays of <codeph>&lt;class T&gt;</codeph> elements.</p> <p>The following

example illustrates the point. It constructs a fixed flat array, a variable

flat array and a packed array of <codeph>&lt;TElement&gt;</codeph> objects.</p> <p>By

taking a <codeph>TArray&lt;TElement&gt;</codeph> argument, the <codeph>CTot::Total()</codeph> member

function can access array elements regardless of the type of array containing

them.</p> <codeblock id="GUID-C5A09CDE-7923-5427-9BB9-0BB518597E0B" xml:space="preserve">class TElement                 // array elements

 {

 public:

  TElement();

  inline TInt GetValue() const;

  void SetValue(TInt aVal);

 private :

  TInt iValue;

 };

</codeblock> <codeblock id="GUID-6FB0C2E8-1548-5723-A82A-DDB62124A869" xml:space="preserve">class CTot : public CBase           

 {

 public :

  void Total(const TArray<TElement>& anArray);

 private :

  TInt iTotalElements;

  TInt iTotalValue;

 };

</codeblock> <codeblock id="GUID-9A356EEC-985D-5BA0-90BE-4C5DFBC536D5" xml:space="preserve">TElement::TElement()

 : iValue(0)

 {}

</codeblock> <codeblock id="GUID-D0614571-E2BB-5DB4-A31F-82273D3745E3" xml:space="preserve">inline TInt TElement::GetValue() const

 {

 return iValue;

 }

</codeblock> <codeblock id="GUID-81D89E93-39DC-5FAF-AD45-D345824B7BA5" xml:space="preserve">void TElement::SetValue(TInt aVal)

 {

 iValue = aVal;

 }

</codeblock> <codeblock id="GUID-0336D0FB-E543-54BC-9A12-77D16340163F" xml:space="preserve">void CTot::Total(const TArray&lt;TElement&gt;&amp; anArray)

 {

 TInt count = anArray.Count();

 for (TInt jj = 0; jj < count; jj++)

  iTotalValue += anArray[jj].GetValue();

 iTotalElements += count;

 }

</codeblock> <p>Then some code using these could be:</p> <codeblock id="GUID-CF9EDB28-FC0F-5F5A-907A-55DA637BF82F" xml:space="preserve">//           main body

CArrayFixFlat<TElement>* fix;

CArrayVarFlat<TElement>* var;

CArrayPakFlat<TElement>* pak;

TElement x;

CTot* ptr;

ptr = new CTot;

fix = new CArrayFixFlat<TElement>(2);

var = new CArrayVarFlat<TElement>(2);

pak = new CArrayPakFlat<TElement>(2);

x.SetValue(1);

fix->AppendL(x);

x.SetValue(2);

var->AppendL(x,sizeof(x));

x.SetValue(3);

pak->AppendL(x,sizeof(x));

ptr->Total(fix->Array());

ptr->Total(var->Array());

ptr-&gt;Total(pak-&gt;Array());</codeblock> <p>Without the use of <codeph>TArray</codeph>,

the <codeph>Total()</codeph> member function would need overloaded variants

to handle all the possible array types which it might expect. The <codeph>CTot</codeph> class

would need redefining as:</p> <codeblock id="GUID-54155741-69E5-5B1B-A1DD-A1A701806BDF" xml:space="preserve">class CTot : public CBase           

 {

 public :

  void Total(const CArrayFixFlat<TElement>& anArray);

  void Total(const CArrayFixSeg<TElement>& anArray);

  void Total(const CArrayVarFlat<TElement>& anArray);

  void Total(const CArrayVarSeg<TElement>& anArray);

  void Total(const CArrayPakFlat<TElement>& anArray);

 private :

  TInt iTotalElements;

  TInt iTotalValue;

 };</codeblock> <p>To allow the <codeph>Total()</codeph> function to handle

arrays composed of different types of element, (i.e. arrays constructed with

different template values), then a separate variant of <codeph>Total()</codeph> is

required for each element type. For example, to handle arrays of <codeph>&lt;TElement1&gt;</codeph> elements

and arrays of <codeph>&lt;TElement2&gt;</codeph> elements, the <codeph>CTot</codeph> class

might be defined as:</p> <codeblock id="GUID-AD19E818-0B43-5C78-88B6-D8E7B82A914B" xml:space="preserve">class CTot : public CBase           

 {

 public :

  void TotalA(const TArray<TElement1>& anArray);

  void TotalB(const TArray<TElement2>& anArray);

 private :

  TInt iTotalElements;

  TInt iTotalValue;

 };</codeblock> <p>One important point to note; the referenced <codeph>TElement</codeph> returned

by <codeph>operator[]</codeph> is declared as <codeph>const</codeph>. This

means that any member function of <codeph>TElement</codeph> must also be declared

as <codeph>const</codeph>, as shown in this example.</p> </section>