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Manipulates string and data buffers.
Descriptors are a family of classes that are used in Symbian OS for string handling. They are used in preference to NULL-terminated C strings. The same classes are used for general binary data.
The basic classification of descriptor types is given below. Concrete descriptor classes implement variations on these basic types for different data widths and for different abilities to modify the data. The names of the concrete classes follow certain naming conventions that modify the basic name given in the table.
Type |
Description |
Basic name |
abstract |
Base interface: allows descriptors of different types to be use polymorphically |
|
buffer |
Stack based: contains the data as part of itself. Buffer descriptors have a maximum length set at compile time. |
|
pointer |
Refer to data stored elsewhere that is not owned by the descriptor |
|
heap |
Refers to data stored on the heap that is owned by the descriptor. The maximum length of this data can be set and changed dynamically. |
Descriptor types can store 8-bit or 16-bit data. These types are
indicated by the convention of appending 8 or 16 on the basic name, e.g.
TDes16
. In practice, the basic names correspond to 16-bit
types, for example TBuf
is defined to be
TBuf16
.
Modifiable descriptor types have an interface that allows callers to alter their contents, such as appending characters.
Non-modifiable descriptor types can have their contents reset, but
not modified. The convention is for non-modifiable types to append a C on the
basic name, e.g. TBufC
.
Heap type descriptors are an exceptional case: they are available
only in the non-modifiable form, but can, nevertheless, be modified through use
of a pointer: see HBufC::Des()
. Alternatively, you can use the
RBuf
descriptor, which is simpler to use than
HBufC
. The general rule is:
use HBufC
for data that rarely changes.
Use RBuf
for data that changes frequently.