Class CBufSeg

class CBufSeg : public CBufBase;

Description

Provides a segmented dynamic buffer.

This class should be used when the object has a long life-time and an unpredictable number of insertions, or there is concern about the performance of insertion and deletion operations into large buffers.

This class is an implementation of the abstract buffer interface provided by CBufBase and uses doubly-linked list of heap cells to contain the data; each cell containing a segment of the buffer.

Its (private) data members include an anchor for the doubly-linked list, and also a reference to the buffer position used by the last operation. This reference acts as a cache; if the next operation uses a similar buffer position, then calculation of the pointer corresponding to its buffer position is much faster.

Derivation

• CBase - Base class for all classes to be instantiated on the heap

• CBufBase - Defines the interface for dynamic buffers

• CBufSeg - Provides a segmented dynamic buffer

Members

Defined in CBufSeg:
BackPtr(), CBufSeg(), Compress(), Delete(), DoInsertL(), NewL(), Ptr(), ~CBufSeg()

Inherited from CBase:
Extension_(), operator new()

Inherited from CBufBase:
ExpandL(), InsertL(), Read(), Reset(), ResizeL(), Size(), Write(), iExpandSize, iSize

IMPORT_C ~CBufSeg();

Description

Destructor.

Frees all resources owned by the object, prior to its destruction.

Specifically, it frees all segments allocated to the buffer.

static IMPORT_C CBufSeg *NewL(TInt anExpandSize);

Description

Allocates and constructs a segmented buffer.

If there is insufficient memory available to allocate the segmented buffer, the function leaves.

Parameters

TInt anExpandSize The granularity of the buffer. Each segment contains (in addition to 16 bytes of overhead) this number of bytes for data. Note: although a value of zero is permitted by this interface, it has no meaning, and risks raising panics later during execution. We suggest that you pass a positive value.

Return value

CBufSeg * If successful, a pointer to the segmented buffer object.

Panic codes

E32USER-CBase 3 if the granularity is negative.

protected: IMPORT_C CBufSeg(TInt anExpandSize);

Description

Parameters

TInt anExpandSize

virtual IMPORT_C void Compress();

Description

Compresses the buffer so as to occupy minimal space.

Fills any space in each segment of the buffer by moving contents from the next segment to the current one. Where this activity results in empty segments, it frees the memory associated with these segments.

virtual IMPORT_C void Delete(TInt aPos, TInt aLength);

Description

Deletes data from the buffer.

During deletion, shuffling is minimised by deleting intermediate segments and allowing segments to contain less data than the buffer granularity.

Parameters

TInt aPos Buffer position where the deletion will begin; must be in the range zero to (Size() minus the length of the data to be deleted). TInt aLength The number of bytes to be deleted.

virtual IMPORT_C TPtr8 Ptr(TInt aPos);

Description

Gets a pointer descriptor to represent the data starting at the specified data byte through to the end of the contiguous region containing that byte.

The time needed for calculation of the pointer depends on how many segments there are in the buffer, and how near the target segment is to the segment which was last used in the buffer.

Parameters

TInt aPos Buffer position: must be in range zero to Size().

Return value

TPtr8 Descriptor representing the data starting at aPos to the end of the contiguous region containing that byte.

virtual IMPORT_C TPtr8 BackPtr(TInt aPos);

Description

Gets a pointer descriptor to represent the data starting at the beginning of the contiguous region containing that byte through to the byte immediately preceding the specified byte.

The descriptor always points to the beginning of the segment containing the specified byte. The time needed for calculation of the pointer depends on how many segments there are in the buffer, and how near the target segment is to the segment which was last used in the buffer.

Parameters

TInt aPos Buffer position: must be in range zero to Size().

Return value

TPtr8 Descriptor representing the back contiguous region.

private: virtual IMPORT_C void DoInsertL(TInt aPos, const TAny *aPtr, TInt aLength);

Description

Parameters

TInt aPos const TAny *aPtr TInt aLength