Currently, each backend has it's own function to verify whether the
object vtable pointer is the expected one. All these functions can be
removed in favor of a single isintance function in the base class,
which takes the expected vtable pointer as a parameter.
Functions which are called through the vtable, don't need to verify the
vtable pointer, and those checks are removed.
The term "backend" can be confusing because it can refer to both the
virtual function table and the device/parser backends. The use of the
term "vtable" avoids this.
The version function requires device specific knowledge to use it (at
least the required buffer size), it is already called internally when
necessary, and only a few backends support it. Thus there is no good
reason to keep it in the high-level public api.
I forgot to update the device and parser initialization functions to
store the context pointer into the objects. As a result, the internal
context pointers were always NULL.
The public api is changed to require a context object for all
operations. Because other library objects store the context pointer
internally, only the constructor functions need an explicit context
object as a parameter.
Adding the "dc_" namespace prefix (which is of course an abbreviation
for libdivecomputer) should avoid conflicts with other libraries. For
the time being, only the high-level device and parser layers are
changed.
The public header files are moved to a new subdirectory, to separate
the definition of the public interface from the actual implementation.
Using an identical directory layout as the final installation has the
advantage that the example code can be build outside the project tree
without any modifications to the #include statements.
To be able to cancel an operation, an application should register a
callback function that returns a non-zero value whenever the active
operaton should be cancelled. A backend can invoke this callback function
to query the application for a pending cancellation request.
Using a resizable memory buffer allows to allocate the right amount of
memory inside the backend, avoiding having to know the required buffer
size in advance.
The DTR line is used to initialize or reset the communication. Toggling
this line before each transfer, rather than doing it once at startup,
allows to perform multiple transfers in the same session.
Moved the initialization of the backend pointers to the beginning of the
source file. Without the need for a tentative definition, the library
can be compiled with a C++ compiler.
When necessary, an output parameter is added to provide the size
information. Status codes are strictly reserved for providing status
information only.
