diff -r 51a74ef9ed63 -r ae94777fff8f Symbian3/SDK/Source/GUID-EA3419BD-D757-5AC3-AE6F-DF21F794AE47.dita --- a/Symbian3/SDK/Source/GUID-EA3419BD-D757-5AC3-AE6F-DF21F794AE47.dita Wed Mar 31 11:11:55 2010 +0100 +++ b/Symbian3/SDK/Source/GUID-EA3419BD-D757-5AC3-AE6F-DF21F794AE47.dita Fri Jun 11 12:39:03 2010 +0100 @@ -1,75 +1,75 @@ - - - - - -Descriptor -basicsThis document describes buffer descriptors, heap descriptors, pointer -descriptors and resizable buffer descriptors. -

Descriptors provide a safe, consistent and economical mechanism for accessing -and manipulating strings and general binary data.

-

A descriptor represents data which can reside in any memory location, either -ROM or RAM. A descriptor object maintains pointer and length information to -describe the data. All access to the data is made through the descriptor object.

-

The area occupied by data represented by a given descriptor is considered -to be non-expandable, even though the length of data represented can shrink -or expand to fill that area.

-

The set of operations which can be performed on data represented by a descriptor -is divided into those that can modify the data and those which provide access -but do not modify the data. This split is reflected in the structure of the -descriptor classes.

-

Operations on data represented by a descriptor are safe. Accidental or -deliberate attempts to access memory outside the data area represented by -a descriptor are caught. An illegal access is treated as bad programming rather -than an environment or resource problem and raises an exception known as a -panic.

-

Descriptors make no distinction between the type of data represented; both -strings and binary data are treated in the same way. Although some operations -on a descriptor are intended to operate on a string, they also work on binary -data. This unifies the handling of both strings and binary data and increases -efficiency by allowing code to be shared. This also means that data can consist -of a mix of string data and binary data.

-

The concrete descriptors that programs create come in four types:

- - - Buffer descriptor - - - - Heap descriptor - - - - Pointer descriptor - - - - Resizable buffer descriptor - - -

Although the four types seem to be different, the underlying class structure -makes such differences transparent allowing them to be treated in the same -way.

-

Descriptor objects generally, behave as built-in types, as they can be -safely created on the program stack and can also be safely orphaned. The heap -descriptor is an exception to this rule.

-

The design also avoids the memory overhead associated with virtual functions.

+ + + + + +Descriptor +basicsThis document describes buffer descriptors, heap descriptors, pointer +descriptors and resizable buffer descriptors. +

Descriptors provide a safe, consistent and economical mechanism for accessing +and manipulating strings and general binary data.

+

A descriptor represents data which can reside in any memory location, either +ROM or RAM. A descriptor object maintains pointer and length information to +describe the data. All access to the data is made through the descriptor object.

+

The area occupied by data represented by a given descriptor is considered +to be non-expandable, even though the length of data represented can shrink +or expand to fill that area.

+

The set of operations which can be performed on data represented by a descriptor +is divided into those that can modify the data and those which provide access +but do not modify the data. This split is reflected in the structure of the +descriptor classes.

+

Operations on data represented by a descriptor are safe. Accidental or +deliberate attempts to access memory outside the data area represented by +a descriptor are caught. An illegal access is treated as bad programming rather +than an environment or resource problem and raises an exception known as a +panic.

+

Descriptors make no distinction between the type of data represented; both +strings and binary data are treated in the same way. Although some operations +on a descriptor are intended to operate on a string, they also work on binary +data. This unifies the handling of both strings and binary data and increases +efficiency by allowing code to be shared. This also means that data can consist +of a mix of string data and binary data.

+

The concrete descriptors that programs create come in four types:

+
    +

  • Buffer descriptors - +where the data is part of the descriptor object and the descriptor object +lives on the program stack.

    • +

  • Heap descriptors - where +the data is part of the descriptor object and the descriptor object lives +on the heap.

    • +

  • Pointer descriptors +- where the descriptor object is separate from the data it represents.

    • +

  • Resizable buffer descriptors +- where the descriptor is separate from the data it represents, and the data +resides in a buffer allocated on the heap.

    • +
+ + Buffer descriptor + + + + Heap descriptor + + + + Pointer descriptor + + + + Resizable buffer descriptor + + +

Although the four types seem to be different, the underlying class structure +makes such differences transparent allowing them to be treated in the same +way.

+

Descriptor objects generally, behave as built-in types, as they can be +safely created on the program stack and can also be safely orphaned. The heap +descriptor is an exception to this rule.

+

The design also avoids the memory overhead associated with virtual functions.

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