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examples/ForumNokia/DescriptorExample/src/DeclaringDescriptors.cpp

/*
 * Copyright © 2008 Nokia Corporation.
 */

#include <e32std.h>
#include <e32base.h>
#include "DescriptorExamples.h"
#include "StringRenderer.h"

// -----------------------------------------------------------------------------
// This example method is documented in header file "DescriptorExamples.h"
// -----------------------------------------------------------------------------
void CDescriptorExamples::ToStack()
    {
    TPtr output( iViewer->GetViewBuffer() );
    
    //Note, You should use the _LIT macro instead of _L
    RenderHeader( _L( "ToStack" ), output );

    // --------------------
    // declare constant buffers to stack as automatic variable:
    // length=0, maxsize=20, data="".
    // Note that these automatic variables consumes stack until the
    // method ends...
    TBufC<20> tbufc20( _L("Hey!") );
    RenderVariableFormatted( tbufc20.Des(), output, KRenderCharacteristics );

    // --------------------
    // declare modifiable buffers to stack as automatic variable:
    // length=0, maxsize=20, data=""
    TBuf<20> tbuf20;
    RenderVariableFormatted( tbuf20, output, KRenderCharacteristics );

    // --------------------
    // declare a non modifying descriptor pointer that points to array in
    // the middle of a temporary buffer: length=3, data="loWo"
    // Example is declared to own code block so automatic variables are
    // deleted when block ends.
        {
        TBuf<20> tmpBuf(_L("HelloWorld"));
        const TText* arrayInBuf = tmpBuf.Ptr(); // point to first char in buffer
        TPtrC partOfBuffer( arrayInBuf + 3, 4 );
        RenderVariableFormatted( tmpBuf, output,
                                 KRenderCharacteristics );
        RenderVariableFormatted( partOfBuffer, output,
                                 KRenderCharacteristics );
        } // tmpBuf, arrayInBuf and partOfBuffer do no more exist in stack

    // --------------------
    // declare modifying buffer pointer pointing to memory
    // in another buffer: length=4, maxSize=5, data=loWo
        {
        // tmpBuf below can't be edited with its methods but we can alter data
        // through modifiable buffer pointer created few lines later
        TBufC<20> tmpBuf(_L("HelloWorld"));
        // Set arrayInBuf to point to first character in buffer. Has to be
        // cast to non const pointer since TPtr expects such (of course)
        TText* arrayInBuf = (TText*)tmpBuf.Ptr();
        TPtr modifyingPointer( arrayInBuf + 3, 4, 5 );
        RenderVariableFormatted( modifyingPointer, output,
                                 KRenderCharacteristics );
        }

    // --------------------
    // declare modifying buffer pointing to a buffer descriptor - instead of
    // of its buffer directrly. The only way to do a such is to call method
    // Des() of non modifiable descriptors buffers TBufC and HBuf.
    // contents of tmpBuf after modification: length=6, maxlength=20,
    // data="HWorld"
        {
        TBufC<20> originalBuf( _L("HelloWorld") );
        TPtr tmpBufPtr = originalBuf.Des();
        // modify the original buffer. Length in both descriptors
        // is updated!
        tmpBufPtr.Delete(1, 4);
        RenderVariableFormatted( originalBuf.Des(), output,
                                 KRenderCharacteristics );
        }
    iViewer->UpdateView();
    }

// -----------------------------------------------------------------------------
// This example method is documented in header file "DescriptorExamples.h"
// -----------------------------------------------------------------------------
void CDescriptorExamples::ToHeapL()
    {
    TPtr output( iViewer->GetViewBuffer() );
    RenderHeader( _L( "ToHeap" ), output );

    // --------------------
    // Allocate heap buffer with buffer size of 512. Factory
    // method LC allocates the object, pushes cleanup item to
    // cleanup stack and returns pointer to allocated object.
    //
    HBufC *hbufc = HBufC::NewLC( 512 );
    RenderVariableFormatted( hbufc->Des(), output, KRenderCharacteristics );

    // --------------------
    // Allocate TBuf descriptor with the same characteristics
    // like example above. Let also the constructor to initialize
    // the buffer with text.
    TBuf<512> *tbuf = new (ELeave) TBuf<512>( _L("Hello World!") );
    // Objects allocated from heap have to be deleted explicitly. Quite good
    // practise is to push every item allocated from heap to cleanup stack and
    // let the last line in method delete all allocated objects with one method
    // call (CleanupStack::PopAndDestroy(count)). If method leaves at the middle
    // of execution, the trap harness deletes automatically all objects pushed
    // to cleanup stack and no memory leaks occur.
    CleanupStack::PushL( tbuf );
    RenderVariableFormatted( *tbuf, output, KRenderCharacteristics );

    // we do no more need allocated objects, so lets remove them from cleanup
    // stack with one method call.
    CleanupStack::PopAndDestroy(2); // hbufc & tbuf
    iViewer->UpdateView();
    }

// -----------------------------------------------------------------------------
// This example method is documented in header file "DescriptorExamples.h"
// -----------------------------------------------------------------------------
void CDescriptorExamples::Literals()
    {
    TPtr output( iViewer->GetViewBuffer() );
    RenderHeader( _L( "Literals" ), output );

    // --------------------
    // Declare variable KLit1 and assing some text to it. _LIT macro
    // evaluates so that static constant variable is declared and
    // initialized with given string data. Since static and constant,
    // it is compiled as part of program binary.
    _LIT( KLit1, "String declared with macro _LIT" );
    RenderVariableFormatted( KLit1, output, KRenderCharacteristics );

    // --------------------
    // Literals can be also created with macro _L. However, it isn't
    // so efficient (refer book "Symbian OS C++ for Mobile Phones"
    // for details). Using it in test code is acceptable.
    TPtrC L1 = _L( "String declared with macro _L" );
    RenderVariableFormatted( L1, output, KRenderCharacteristics );

    // --------------------
    // Let's declare a literal that contains euro sign (0x20AC).Since it
    // doesn't exist in many 8 bit encodings , we declare it as 'e' when
    // building non-unicode build
#ifdef _UNICODE
    // note that in unicode literal the unicode chars can be declared
    // by passing the unicode number of the character as hexadecimal number
    _LIT( KLitEuro, "I won 166\x20AC from lottery!" );
#else
    _LIT( KLitEuro, "I won 166e from lottery!" );
#endif
    RenderVariableFormatted( KLitEuro, output, KRenderCharacteristics );
    iViewer->UpdateView();
    }

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Copyright ©2010 Nokia Corporation and/or its subsidiary(-ies).
All rights reserved. Unless otherwise stated, these materials are provided under the terms of the Eclipse Public License v1.0.