heapbuffer.cpp

symbian c++ example buffering and string heap buffer

// HeapBuffer.cpp
//
// Copyright (C) Symbian Software Ltd 2000-2005.  All rights reserved.

// Examples to demonstrate the basic ideas of heap buffer descriptors.

#include "CommonFramework.h"

//
// Common literal text
//
_LIT(KTxtHelloWorld,"Hello World!");
_LIT(KTxtHelloWorldMorning,"Hello World! Morning");
_LIT(KTxtAndHi," & Hi");

//
// Common Format strings
//
_LIT(KCommonFormat1,"Size()=%d;\nMaxLength()=%d\n");
_LIT(KCommonFormat2,"Ptr()=%x; Length()=%d; ");
_LIT(KCommonFormat5,"Ptr()=%x; Length()=%d; Size()=%d\n");


// Do the example
LOCAL_C void doExampleL()
    {
	
				// An HBufC is always constructed on the heap
				// using the static New(), NewL() or NewLC()
	HBufC* buf;

				// Construct an HBufC.
				// This descriptor can hold up to 15 data 
				// items.
				// The current length is zero
	buf  = HBufC::NewL(15);
	CleanupStack::PushL(buf);

				// Note, we could replace the above two lines of code
				// with the single line: buf  = HBufC::NewLC(15);


				// Show 1. Content
				//      2. address of descriptor
				//      3. address of descriptor data area
				//      4. length of descriptor
				//      5. size of descriptor
				// The address of the descriptor data area
				// is offset 4 from the start of the 
				// descriptor itself.
	_LIT(KFormat10,"\"%S\"; descriptor at %x; ");
	console->Printf(KFormat10,buf,buf);
	console->Printf(KCommonFormat5,buf->Ptr(),buf->Length(),buf->Size());
					  	 
				// Set up some data into the HBufC 
	*buf = KTxtHelloWorld;          // "Hello World!"

				// Show 1. Content
				//      2. length of descriptor
				//      3. size of descriptor
	_LIT(KFormat9,"\"%S\"; ");
	console->Printf(KFormat9,buf);
	_LIT(KFormat8,"Length()=%d; Size()=%d\n");
	console->Printf(KFormat8,buf->Length(),buf->Size());

				// Now want to replace the text with:
				// "Hello World! Morning"
				// Resulting length would be > 15
				// So, reallocate the HBufc first
				// to make it bigger

	buf = buf->ReAllocL(20);

	 			// Assign the new text.
	*buf = KTxtHelloWorldMorning;   // "Hello World! Morning"

	 			// Show it
	_LIT(KFormat7,"\n\"%S\"; \n(1st realloc') desc'at %x; ");
	console->Printf(KFormat7,buf,buf);
	console->Printf(KCommonFormat5,buf->Ptr(),buf->Length(),buf->Size());			

				// buf may point to the same area as before.
				// In general, this is not the case so DO 
				// NOT ASSUME. 
	
	buf = buf->ReAllocL(22);
	_LIT(KFormat6,"\n\"%S\"; \n(2nd realloc') desc'at %x; ");
	console->Printf(KFormat6,buf,buf);
	console->Printf(KCommonFormat5,buf->Ptr(),buf->Length(),buf->Size());
	
				// The Des() function returns a TPtr to the
				// HBufC.
				// The HBufC data can be changed through 
				// the TPtr.
				// The maximum length of the TPtr is 
				// determined from the size of the cell 
				// allocated to the data area of the HBufC.
				// In this example, the value has been rounded 
				// up to 24.
	TPtr ptr = buf->Des();

	_LIT(KFormat11,"TPtr descriptor at %x; ");
	console->Printf(KFormat11,&ptr);
	console->Printf(KCommonFormat2,ptr.Ptr(),ptr.Length());
	console->Printf(KCommonFormat1,ptr.Size(),ptr.MaxLength());

				// Now change the HBufC data through
				// the TPtr. This is OK provided the length
				// of the changed data does not exceed the 
				// maximum length.
				//
				// The following change deletes the last 
				// nine characters and then appends 
				// the characters " & Hi".
				//
				// Note that the length of both the HBufC 
				// and the TPtr reflect the changed data.
	
	ptr.Delete((ptr.Length()-9),9);
    ptr.Append(KTxtAndHi); // " & Hi"
	
				// Look at it from HBufC's viewpoint
	_LIT(KFormat4,"\n\"%S\";\nHBufC descriptor at %x; ");
	console->Printf(KFormat4,buf,buf);

	console->Printf(KCommonFormat5,buf->Ptr(),buf->Length(),buf->Size());

				// Look at it from TPtr's viewpoint
	_LIT(KFormat3,"\"%S\"; \nTPtr  descriptor at %x; ");
	console->Printf(KFormat3,&ptr,&ptr);
	console->Printf(KCommonFormat2,ptr.Ptr(),ptr.Length());
	console->Printf(KCommonFormat1,ptr.Size(),ptr.MaxLength());
				// Pop the HBufC off the cleanup stack
				// and destroy it (i.e. the HBufC)
	CleanupStack::PopAndDestroy();
    }