Class TStreamBuf

class TStreamBuf : public MStreamBuf;

Description

Adds buffering capabilities to a stream buffer

The class provides pointers to mark out the current read and write areas within the intermediate buffer. The class also defines the pure virtual functions UnderflowL() and OverflowL() which must be provided by a derived class.

Streams which have buffering capabilities derive from this class, otherwise they derive from MStreamBuf.

Note that the class does not provide the buffer; this is left to the class derived from it. For example, the memory buffer classes use the memory area directly, the file buffer class allocate a heap cell to use as a buffer.

Derivation

• MStreamBuf - A stream buffer that provides a generic I/O interface for streamed data

• TStreamBuf - Adds buffering capabilities to a stream buffer

Members

Defined in TStreamBuf:
Avail(), Avail(), Avail(), DoReadL(), DoReadL(), DoWriteL(), DoWriteL(), End(), End(), End(), OverflowL(), Ptr(), Ptr(), Ptr(), SetBuf(), SetBuf(), SetBuf(), SetEnd(), SetEnd(), SetEnd(), SetPtr(), SetPtr(), SetPtr(), TArea, TStreamBuf(), UnderflowL()

Inherited from MStreamBuf:
Close(), DoRelease(), DoSeekL(), DoSynchL(), ERead, EWrite, PushL(), Read(), ReadL(), Release(), SeekL(), SizeL(), Synch(), SynchL(), TMark, TRead, TWrite, TellL(), Write(), WriteL()

See also:

• UnderflowL()
• OverflowL()

protected: IMPORT_C TStreamBuf();

Description

Sets the pointers that mark out the read and write areas within the intermediate buffer to null.

protected: IMPORT_C void SetBuf(TArea anArea, TUint8 *aPtr, TUint8 *anEnd);

Description

Sets the start and end points of the read and/or the write area within the intermediate buffer.

A start point is always within an area; an end point is always the first byte beyond the end of an area.

Parameters

TArea anArea The areas within the intermediate buffer for which the start and end points are to be set. These can be the read area and/or the write area, as indicated by the ERead and EWrite bits. Only these bits can be set, otherwise the function raises a STORE-Stream 17 panic. TUint8 *aPtr The start point. TUint8 *anEnd The end point.

See also:

• MStreamBuf::TRead
• MStreamBuf::TWrite

protected: IMPORT_C void SetPtr(TArea anArea, TUint8 *aPtr);

Description

Sets the start point of the read and/or the write area within the intermediate buffer.

A start point is always within an area.

Parameters

TArea anArea The areas within the intermediate buffer for which the start point is to be set. These can be the read area and/or the write area, as indicated by the ERead and EWrite bits. Only these bits can be set, otherwise the function raises a STORE-Stream 17 panic. TUint8 *aPtr The start point.

See also:

• MStreamBuf::TRead
• MStreamBuf::TWrite

protected: IMPORT_C void SetEnd(TArea anArea, TUint8 *anEnd);

Description

Parameters

TArea anArea TUint8 *anEnd

protected: IMPORT_C TUint8 *Ptr(TArea anArea) const;

Description

Gets the current start point of the read or write area within the intermediate buffer.

Parameters

TArea anArea The area within the intermediate buffer for which the start point is to be fetched. This can be either the read area or the write area, as indicated by the ERead and EWrite bits. Only one of these can be set, otherwise the function raises a STORE-Stream 17 panic.

Return value

TUint8 * The start point.

See also:

• MStreamBuf::TRead
• MStreamBuf::TWrite

protected: IMPORT_C TUint8 *End(TArea anArea) const;

Description

Gets the current end point of the read or write area within the intermediate buffer.

An end point is always the first byte beyond the end of an area.

Parameters

TArea anArea The area within the intermediate buffer for which the end point is to be fetched. This can be either the read area or the write area, as indicated by the ERead and EWrite bits. Only one of these can be set, otherwise the function raises a STORE-Stream 17 panic.

Return value

TUint8 * The end point.

protected: IMPORT_C TInt Avail(TArea anArea) const;

Description

Gets the number of bytes available in the read or write area within the intermediate buffer.

Parameters

TArea anArea The area within the intermediate buffer for which the number of available bytes is to be fetched. This can be either the read area or the write area, as indicated by the ERead and EWrite bits. Only one of these can be set, otherwise the function raises a STORE-Stream 17 panic.

Return value

TInt The number of bytes available.

protected: virtual IMPORT_C TInt DoReadL(TAny *aPtr, TInt aMaxLength);

Description

Reads data from the intermediate buffer into the specified memory location.

The function calls the virtual function UnderfLowL() to give concrete implementations the chance to refill the intermediate buffer, and satisfy the caller's requirements.

This implementation overrides the one supplied by the base class MStreamBuf, and is called by, MStreamBuf::ReadL(TAny*,TInt).

Parameters

TAny *aPtr A pointer to the target memory location for the data read from the intermediate buffer. TInt aMaxLength The maximum number of bytes to be read.

Return value

TInt The number of bytes read. This may be less than the amount requested.

See also:

• MStreamBuf::ReadL()
• MStreamBuf::DoReadL()

protected: virtual IMPORT_C TStreamTransfer DoReadL(MStreamInput &anInput, TStreamTransfer aTransfer);

Description

Reads data from the intermediate buffer and, if necessary, any remaining data from the stream to the specified target stream input object.

It is called by ReadL(MStreamInput&,TStreamTransfer).

The intermediate buffer is emptied first by calling the target stream input's PushL() function, which performs the read from intermediate buffer operation. Any remaining data is then read from the stream by calling the target stream object's ReadFromL() function, which performs the read from stream operation.

This implementation is called for streams that have buffering capabilities and are derived from this class.

Parameters

MStreamInput &anInput The target stream input object. TStreamTransfer aTransfer A stream transfer object defining the amount of data available to be written.

Return value

TStreamTransfer The amount of data that was not consumed.

See also:

• MStreamInput::ReadFromL()
• MStreamInput::PushL()

protected: virtual IMPORT_C void DoWriteL(const TAny *aPtr, TInt aLength);

Description

Writes data from the specified memory location into the intermediate buffer.

The function calls the virtual function OverfLowL() to give concrete implementations the chance to forward the intermediate buffer content to its destination.

This implementation overrides the one supplied by the base class MStreamBuf, and is called by MStreamBuf::WriteL(const TAny*,TInt).

Parameters

const TAny *aPtr A pointer to the source memory location for the data to be written to the intermediate buffer. TInt aLength The number of bytes to be written.

See also:

• MStreamBuf::WriteL()
• MStreamBuf::DoWriteL()

protected: virtual IMPORT_C TStreamTransfer DoWriteL(MStreamOutput &anOutput, TStreamTransfer aTransfer);

Description

Parameters

MStreamOutput &anOutput TStreamTransfer aTransfer

Return value

TStreamTransfer

protected: inline void SetBuf(TRead, TUint8 *aPtr, TUint8 *anEnd);

Description

Sets the start and end points of the read area within the intermediate buffer.

A start point is always within an area; an end point is always the first byte beyond the end of an area.

Parameters

TRead TUint8 *aPtr The start point. TUint8 *anEnd The end point.

See also:

• MStreamBuf::TRead

protected: inline void SetBuf(TWrite, TUint8 *aPtr, TUint8 *anEnd);

Description

Sets the start and end points of the write area within the intermediate buffer.

A start point is always within an area; an end point is always the first byte beyond the end of an area.

Parameters

TWrite TUint8 *aPtr The start point. TUint8 *anEnd The end point.

See also:

• MStreamBuf::TWrite

protected: inline void SetPtr(TRead, TUint8 *aPtr);

Description

Sets the start point of the write area within the intermediate buffer.

A start point is always within an area.

Parameters

TRead TUint8 *aPtr The start point.

See also:

• MStreamBuf::TWrite

protected: inline void SetPtr(TWrite, TUint8 *aPtr);

Description

Sets the start point of the write area within the intermediate buffer.

A start point is always within an area.

Parameters

TWrite TUint8 *aPtr The start point.

See also:

• MStreamBuf::TWrite

protected: inline void SetEnd(TRead, TUint8 *anEnd);

Description

Parameters

TRead TUint8 *anEnd

protected: inline void SetEnd(TWrite, TUint8 *anEnd);

Description

Parameters

TWrite TUint8 *anEnd

protected: inline TUint8 *Ptr(TRead) const;

Description

Gets the current start point of the read area within the intermediate buffer.

Parameters

TRead

Return value

TUint8 * The start point.

See also:

• MStreamBuf::TRead

protected: inline TUint8 *Ptr(TWrite) const;

Description

Gets the current start point of the write area within the intermediate buffer.

Parameters

TWrite

Return value

TUint8 * The start point.

See also:

• MStreamBuf::TWrite

protected: inline TUint8 *End(TRead) const;

Description

Gets the current end point of the read area within the intermediate buffer.

An end point is always the first byte beyond the end of an area.

Parameters

TRead

Return value

TUint8 * The end point.

See also:

• MStreamBuf::TRead

protected: inline TUint8 *End(TWrite) const;

Description

Gets the current end point of the write area within the intermediate buffer.

An end point is always the first byte beyond the end of an area.

Parameters

TWrite

Return value

TUint8 * The end point.

See also:

• MStreamBuf::TWrite

protected: inline TInt Avail(TRead) const;

Description

Gets the number of bytes available in the read area within the intermediate buffer.

Parameters

TRead

Return value

TInt The number of bytes available.

See also:

• MStreamBuf::TRead

protected: inline TInt Avail(TWrite) const;

Description

Gets the number of bytes available in the write area within the intermediate buffer.

Parameters

TWrite

Return value

TInt The number of bytes available.

See also:

• MStreamBuf::TWrite

private: virtual TInt UnderflowL(TInt aMaxLength)=0;

Description

Re-fills the intermediate buffer and resets the start and end points of the read area.

The implementation of this function depends on the way the stream itself is implemented. For example, the in-memory streams have simple implementations.

Parameters

TInt aMaxLength The maximum amount of data required for the intermediate buffer.

Return value

TInt The amount of data available in the intermediate buffer.

private: virtual void OverflowL()=0;

Description

Empties the intermediate buffer and resets the start and end points of the write area.

The implementation of this function depends on the way the stream itself is implemented. For example, the in-memory streams have simple implementations.

protected: typedef TInt TStreamBuf::TArea;

Description

Used to identify the type of area within an intermediate buffer.

The type is used by functions of this class that set or get pointers into the intermediate buffer.

The type uses the ERead and EWrite enumeration values, as bit flags, to identify the read and write areas respectively.

ERead is an MStreamBuf::TRead enumerator. EWrite is an MStreamBuf::EWrite enumerator.

See also:

• MStreamBuf::TRead
• MStreamBuf::TWrite