Use TDes for interfaces which take narrow or wide (Unicode) text, depending on the build variant.
An interface which needs to access
and modify either narrow text or wide (Unicode) text, depending on
the build variant, uses a TDes as the argument
type. All build independent concrete descriptors are derived from TDes which means that the interface can accept any build
independent descriptor.
The following code fragment shows the most common function prototype pattern.
void ClassX::foo(TDes& anArg);
The use of TDes means that data can be accessed
and modified through the descriptor.
If the interface is to
handle explicit 8 bit or explicit 16 bit data, regardless of the build
variant, then use TDes8 or TDes16 instead.