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<concept xml:lang="en" id="GUID-2277BB1C-C04D-56C8-9B9B-FBC2EDCA9B07"><title>How to externalise and internalise compound objects</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>Compound objects can be externalised and internalised. The only assumption is that all component objects (and their component objects) must be capable of being externalised and internalised.</p> <p>In this example, a compound object, an instance of the <codeph>CCompound</codeph> class, is externalised to, and internalised from, a single stream. The class is defined as:</p> <codeblock id="GUID-E6ACB6CF-C933-5C11-A773-F25EB05F8E73" xml:space="preserve">class CCompound : public CBase

    {

public :

    void ExternalizeL(RWriteStream& aStream) const;

    void ExternalizeL(RReadStream& aStream);

    ...

    CClassA* iCa;

    CClassB* iCb;

    TClassC  iTc;

    };</codeblock> <section><title>Externalising</title> <p>The preferred implementation of the <codeph>ExternalizeL()</codeph> function is:</p> <codeblock id="GUID-ED0746BB-7D2F-5274-BAF6-3FBF1781A0C3" xml:space="preserve">void CCompound::ExternalizeL(RWriteStream&amp; aStream) const

    {

    aStream << *iCa;

    aStream << *iCb;

    aStream << iTc;

    }</codeblock> <p>The following implementation is also correct:</p> <codeblock id="GUID-2939633F-6FEB-596C-AE2F-DBBDB879B3E3" xml:space="preserve">void CCompound::ExternalizeL(RWriteStream&amp; aStream) const

    {

    iCa->ExternalizeL(aStream);

    iCb->ExternalizeL(aStream);

    iTc.ExternalizeL(aStream);

    }</codeblock> </section> <section><title>Internalising</title> <p>The preferred implementation of the <codeph>InternalizeL()</codeph> function is:</p> <codeblock id="GUID-60D0A0F9-A716-5EE2-AF31-D9927723BA12" xml:space="preserve">void CCompound::InternalizeL(RReadStream&amp; aStream)

    {

    aStream >> *iCa;

    aStream >> *iCb;

    aStream >>  iTc;

    }</codeblock> <p>The following implementation is also correct:</p> <codeblock id="GUID-E3DF0907-BE25-5D4E-A6FD-720CD70F9033" xml:space="preserve">void CCompound::InternalizeL(RReadStream&amp; aStream)

    {

    iCa->InternalizeL(aStream);

    iCb->InternalizeL(aStream);

    iTc.InternalizeL(aStream);