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<task id="GUID-C3086910-D7B4-5549-BF65-374C8B602E8F" xml:lang="en"><title>Compressing

and Decompressing Memory Streams </title><shortdesc>The Zip Compression Library, EZLib provides stream compression

and decompression functionality for the Symbian platforms. This tutorial summarizes

the procedure involved in the compression and decompression of memory streams

by EZLib. </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody>

<context id="GUID-FF2527FF-1DFC-59B3-AC6D-5D7FDF7CCDF7"><p>The functions used

for memory stream compression and decompression are provided by the <xref href="GUID-AEF8BCC8-6B24-3D59-AD3A-17B5203B3AA5.dita"><apiname>CEZCompressor</apiname></xref> class. </p> <p>The

compression can be executed in single or multiple steps. This is depenedent

on the buffer size of the memory stream. Small buffers are compressed in a

single step. Larger buffers are compressed in small chunks repeatedly till

the entire buffer is compressed. Clients must respond to callbacks from the

library to provide information and resources required to complete the task. </p> </context>

<steps id="GUID-9F423FB8-8AC5-54EC-B879-04EFA022FD38">

<step id="GUID-D640BCC5-5F5D-5377-9553-F86F5E5D0D56"><cmd/>

<info>Define a buffer manager that implements <xref href="GUID-B90BA6D6-72A2-3EB8-B8EF-CD5408107A9E.dita"><apiname>MEZBufferManager</apiname></xref>. </info>

</step>

<step id="GUID-C8020D99-632E-578A-85A4-4934380A0FD2"><cmd/>

<info>Create an instance of the classs <xref href="GUID-AEF8BCC8-6B24-3D59-AD3A-17B5203B3AA5.dita"><apiname>CEZCompressor</apiname></xref>. </info>

<substeps id="GUID-F4B79439-492C-56A1-A1D9-D92139842405">

<substep id="GUID-C43B76C8-7A9A-5F41-9A9F-210A9267D50E"><cmd/>

<info>Invoke <xref href="GUID-AEF8BCC8-6B24-3D59-AD3A-17B5203B3AA5.dita#GUID-AEF8BCC8-6B24-3D59-AD3A-17B5203B3AA5/GUID-8A60D49C-5E3A-3CF8-9738-B53E7439910A"><apiname>CEZCompressor::CompressL()</apiname></xref> for small buffers. </info>

</substep>

<substep id="GUID-06D723F2-2B7A-5865-B32F-945CE361A4E9"><cmd/>

<info>Invoke <xref href="GUID-AEF8BCC8-6B24-3D59-AD3A-17B5203B3AA5.dita#GUID-AEF8BCC8-6B24-3D59-AD3A-17B5203B3AA5/GUID-03E4E3A2-3830-3209-9D7B-A2238B5AF219"><apiname>CEZCompressor::DeflateL()</apiname></xref> repeatedly on larger

buffers until the entire buffer is compressed. </info>

</substep>

</substeps>

<stepxmp><codeblock xml:space="preserve">class CBufferManager : public CBase, public MEZBufferManager

    {

public:

  CBufferManager* CBufferManager::NewLC();

  CBufferManager* CBufferManager::NewL();

    ~CBufferManager();

    void InitializeL(CEZZStream &aZStream);

    void NeedInputL(CEZZStream &aZStream);

    void NeedOutputL(CEZZStream &aZStream);

    void FinalizeL(CEZZStream &aZStream);

    };

CBufferManager* CBufferManager::NewLC()

    {

    CBufferManager* bm = new (ELeave) CBufferManager();

    CleanupStack::PushL(bm);

    return bm;

    }

CBufferManager* CBufferManager::NewL()

    {

    CBufferManager* bm = new (ELeave) CBufferManager();

    CleanupStack::PushL(bm);

    CleanupStack::Pop();

    return bm;

    }

static void doExampleL()

    {

  CBufferManager* bm = CBufferManager::NewLC();

  //TInt aLevel = EDefaultCompression, TInt aWindowBits = EMaxWBits, TInt aMemLevel = EDefMemLevel, TStrategy aStrategy = EDefaultStrategy);

  CEZCompressor* iCEZCompressor = CEZCompressor::NewLC(*bm); // all other flag values are default in its constructer

  while(icompressor->DeflateL())

        {       

        }     

  CleanupStack::PopAndDestroy(2);

    }

</codeblock></stepxmp>

</step>

</steps>

<postreq id="GUID-4B702763-6D4E-5C32-803B-042024622BAE"><p>To decompress the

memory streams: </p> <ol id="GUID-F4AEDE06-67FC-5624-9D36-FC08D5B460C2">

<li id="GUID-5F44590E-8F53-5B75-ADC9-59073140BA57"><p>Define a buffer manager

that implements <xref href="GUID-B90BA6D6-72A2-3EB8-B8EF-CD5408107A9E.dita"><apiname>MEZBufferManager</apiname></xref>. </p> </li>

<li id="GUID-014484C5-7F1A-5350-B0AD-383091DDA300"><p>Create an instance of

the classs <xref href="GUID-BC3CEC02-B747-38FB-8B35-E7390DB06E35.dita"><apiname>CEZDecompressor</apiname></xref>. </p> </li>

<li id="GUID-EAE82B73-E86B-5E81-8E19-22FCD5EA95AC"><p>Invoke <xref href="GUID-BC3CEC02-B747-38FB-8B35-E7390DB06E35.dita#GUID-BC3CEC02-B747-38FB-8B35-E7390DB06E35/GUID-D9133787-E96C-3E9B-8991-0F0184C7AE7E"><apiname>CEZDecompressor::DecompressL()</apiname></xref> for

small buffers. </p> <p>Invoke <xref href="GUID-BC3CEC02-B747-38FB-8B35-E7390DB06E35.dita#GUID-BC3CEC02-B747-38FB-8B35-E7390DB06E35/GUID-0AC99B66-412B-3CCF-84DA-D7BC0F0D32B2"><apiname>CEZDecompressor::InflateL()</apiname></xref> repeatedly

on larger buffers until the entire buffer is compressed. </p> </li>

</ol> </postreq>