Class HBufC8

HBufC8

Support

Supported from 5.0

Description

8 bit heap descriptor. This is a descriptor class which provides a buffer of fixed length, allocated on the heap, for containing and accessing data.

The class intended for instantiation. The 8 bit data that the descriptor represents is part of the descriptor object itself.

Heap descriptors have the important property that they can be made larger or smaller, changing the size of the data area. This is achieved by reallocating the descriptor. Unlike the behaviour of dynamic buffers, reallocation is not done automatically.

Data is intended to be accessed, but not modified; however, it can be completely replaced using the assignment operators of this class. The base class provides the functions through which the data is accessed.

Derivation

HBufC8 8 bit heap descriptor TBufCBase8 Base class used in the derivation of TBufC8 and HBufC8 TDesC8 Abstract base class for 8 bit non-modifiable descriptors

Defined in HBufC8:
Des(), New(), NewL(), NewLC(), NewMax(), NewMaxL(), NewMaxLC(), ReAlloc(), ReAllocL(), operator=()

Inherited from TDesC8:
Alloc(), AllocL(), AllocLC(), Compare(), CompareC(), CompareF(), Find(), FindC(), FindF(), Left(), Length(), Locate(), LocateF(), LocateReverse(), LocateReverseF(), Match(), MatchC(), MatchF(), Mid(), Ptr(), Right(), Size(), operator!=(), operator<(), operator<=(), operator==(), operator>(), operator>=(), operator[]()

See also:

• TPtr8
• TDesC8

static HBufC8* New(TInt aMaxLength);

Description

Create heap descriptor. Constructs, and returns a pointer to, a new 8 bit heap descriptor that has the specified maximum length.

The heap descriptor is empty and its length is zero.

Data can, subsequently, be assigned into it using the assignment operators.

Parameters

TInt aMaxLength The maximum length of data that the descriptor can represent. This value must be non-negative otherwise the function raises a USER 30 panic.

Return value

HBufC8* A pointer to the new 8 bit heap descriptor.NULL, if the 8 bit heap descriptor cannot be created.

See also:

• HBufC8::operator=()

static HBufC8* NewL(TInt aMaxLength);
static HBufC8* NewL(RReadStream& aStream,TInt aMaxLength);

Description

Constructs, and returns a pointer to, a new 8 bit heap descriptor that has the specified maximum length; leaves on failure.

Data can be assigned to the new descriptor from the specified stream. This variant assumes that the stream contains both the length of the data followed by the data itself.

The heap descriptor is empty when the non-streamed variant function is used and its length is zero. Data can, subsequently, be assigned into it using the assignment operators.

To use the streamed variant, project files must also link against estor.lib.

Note that the resulting length of the descriptor's data area may be larger than specified, depending on the way memory allocation is implemented, but is guaranteed to be not less than that requested.

Parameters

TInt aMaxLength The maximum length of data that the descriptor can represent. This value must be non-negative otherwise the function raises a USER 30 panic. RReadStream& aStream The stream from which the length of the new descriptor and the data to be assigned to the new descriptor, are taken.

Return value

HBufC8* A pointer to the new 8 bit heap descriptor. The function leaves, if the new 8 bit heap descriptor cannot be created. The streamed variant leaves with KErrOverflow if the length of the new descriptor is greater than the maximum length.

See also:

• HBufC8::operator=()

static HBufC8* NewLC(TInt aMaxLength);
static HBufC8* NewLC(RReadStream &aStream,TInt aMaxLength);

Description

Constructs, adds the pointer onto the cleanup stack and returns a pointer to, a new 8 bit heap descriptor that has the specified maximum length; leaves on failure.

Data can be assigned to the new descriptor from the specified stream. This variant assumes that the stream contains both the length of the data followed by the data itself.

The heap descriptor is empty when the non-streamed variant function is used and its length is zero. Data can, subsequently, be assigned into it using the assignment operators.

To use the streamed variant, project files must also link against estor.lib.

Parameters

TInt aMaxLength The maximum length of data that the descriptor can represent. This value must be non-negative otherwise the function raises a USER 30 panic. RReadStream& aStream The stream from which the length of the new descriptor and the data to be assigned to the new descriptor, are taken.

Return value

HBufC8* A pointer to the new 8 bit heap descriptor. This is also put onto the cleanup stack. The function leaves, if the new 8 bit heap descriptor cannot be created. The streamed variant leaves with KErrOverflow if the length of the new descriptor is greater than the maximum length.

See also:

• HBufC8::operator=()

static HBufC8* NewMax(TInt aMaxLength);

Description

Creates a heap descriptor. Constructs, and returns a pointer to, a new 8 bit heap descriptor that has the specified maximum length.

No data is assigned into the new descriptor but its length is set to the same value as the specified maximum length.

Data can, subsequently, be assigned into it using the assignment operators.

Parameters

TInt aMaxLength The maximum length of data that the descriptor can represent. This value must be non-negative otherwise the function raises a USER 30 panic.

Return value

HBufC8* A pointer to the new 8 bit heap descriptor.NULL, if the new 8 bit heap descriptor cannot be created.

See also:

• HBufC8::operator=()

static HBufC8* NewMaxL(TInt aMaxLength);

Description

Constructs, and returns a pointer to, a new 8 bit heap descriptor that has the specified maximum length; leaves on failure.

No data is assigned into the new descriptor but its length is set to the same value as the specified maximum length.

Data can, subsequently, be assigned into it using the assignment operators.

Parameters

TInt aMaxLength The maximum length of data that the descriptor can represent. This value must be non-negative otherwise the function raises a USER 30 panic.

Return value

HBufC8* A pointer to the new 8 bit heap descriptor. The function leaves, if the new 8 bit heap descriptor cannot be created.

See also:

• HBufC8::operator=()

static HBufC8* NewMaxLC(TInt aMaxLength);

Description

Constructs, adds the pointer onto the cleanup stack and returns a pointer to, a new 8 bit heap descriptor that has the specified maximum length; leaves on failure.

No data is assigned into the new descriptor but its length is set to the same value as the specified maximum length.

Data can, subsequently, be assigned into it using the assignment operators.

Parameters

TInt aMaxLength The maximum length of data that the descriptor can represent. This value must be non-negative otherwise the function raises a USER 30 panic.

Return value

HBufC8* A pointer to the new 8 bit heap descriptor. This is also put onto the cleanup stack. The function leaves, if the new 8 bit heap descriptor cannot be created.

See also:

• HBufC8::operator=()

HBufC8* ReAlloc(TInt aMaxLength);

Description

Expands or contracts the heap descriptor.

This is done by:

• creating a new heap descriptor.

• copying the original data into the new descriptor.

• deleting the original descriptor.

Parameters

TInt aMaxLength The maximum length of data that the new descriptor is to represent. This value must be non-negative otherwise the function raises a USER 30 panic. This value must not be less than the length of the data otherwise the function raises a USER 26 panic.

Return value

HBufC8* A pointer to the new expanded or contracted 8 bit heap descriptor. The original descriptor is deleted.NULL, if the new 8 bit heap descriptor cannot be created. The original descriptor remains unchanged.

HBufC8* ReAllocL(TInt aMaxLength);

Description

Expand or contract the descriptor; leave on failure. This is done by:

• creating a new heap descriptor.

• copying the original data into the new descriptor.

• deleting the original descriptor.

Parameters

TInt aMaxLength The maximum length of data that the new descriptor is to represent. This value must be non-negative otherwise the function raises a USER 30 panic. This value must not be less than the length of the data otherwise the function raises a USER 26 panic.

Return value

HBufC8* A pointer to the new expanded or contracted 8 bit heap descriptor. The original descriptor is deleted. The function leaves, if the new 8 bit heap descriptor cannot be created. The original descriptor remains unchanged.

HBufC8& operator=(const HBufC8& aLcb);
HBufC8& operator=(const TDesC8& aDes);
HBufC8& operator=(const TUint8* aString);

Description

Copy and replace data. Copies data into this 8 bit heap descriptor replacing any existing data. The length of this descriptor is set to reflect the new data.

Parameters

const HBufC8& aLcb The source 8 bit heap descriptor. The length of the data must not be greater than the length of the target descriptor otherwise the operator raises a USER 23 panic. const TDesC8& aDes An 8 bit non-modifiable descriptor. The length of the data cannot be greater than the maximum length of the target descriptor otherwise the function raises a USER 23 panic. const TUint8* aString A pointer to a zero-terminated string. The length of the string, excluding the zero terminator, must not be greater than the maximum length of the target descriptor, otherwise the function raises a USER 23 panic.

Return value

HBufC8& A reference to this 8 bit heap descriptor.

TPtr8 Des();

Description

Return an 8 bit modifiable pointer descriptor. Creates and returns an 8 bit modifiable pointer descriptor for the data represented by this 8 bit heap descriptor.

The content of a heap descriptor normally cannot be altered, other than by complete replacement of the data. Creating a modifiable pointer descriptor provides a way of changing the data.

The modifiable pointer descriptor is set to point to this heap descriptor's data.

The length of the modifiable pointer descriptor is set to the length of this heap descriptor.

The maximum length of the modifiable pointer descriptor is set to the length of the heap descriptor's data area.

When data is modified through this new pointer descriptor, the lengths of both it and this heap descriptor are changed.

Note that it is a common mistake to use Des() to create a TDesC8& reference. While not incorrect, it is simpler and much more efficient to simply dereference the heap descriptor.

Return value

TPtr8 An 8 bit modifiable pointer descriptor representing the data in this 8 bit heap descriptor.