Abstract +base descriptor classes

The concrete descriptor classes are all derived from a set of base classes. +The base classes are abstract and implement nearly most of the behaviour of +descriptors. They are:

The abstract non-modifiable descriptor class

The +class has a data member containing the length of the data represented by the +serived concrete descriptor. It also provides the set of functions through +which data can be accessed but not modified.

This class is supplied +in two variants:

the 16 bit variant, +a TDesC16, to handle Unicode strings.
the 8 bit variant, a TDesC8, +to handle non-Unicode strings and binary data.

There is also a build independent type, TDesC. This +is the type which is most commonly used in program code; the appropriate variant +is selected at build time.

An explicit 8 bit variant is chosen when +handling binary data. The explicit 16 bit variant is rarely used.

The abstract modifiable descriptor class

The class +has a data member containing the maximum length of data that the descriptor +is capable of representing. It also provides the set of functions through +which data can be modified.

This class is supplied in two variants:

the 16 bit variant, +a TDes16, to handle Unicode strings.
the 8 bit variant, a TDes8, +to handle non-Unicode strings and binary data.

There is also a build independent type, TDes. This +is the type which is most commonly used in program code; the appropriate variant +is selected at build time.

An explicit 8 bit variant is chosen when +handling binary data. The explicit 16 bit variant is rarely used.