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9.5. Implementation
be discussed in certain detail.
9.5.3. openETCS Generator Implementation
Obviously, CCPPGenerator is the most complex generator class for creating the source code,
which instantiates the classes of the openETCS domain framework. Since nearly all objects in
the openETCS C++ abstract syntax model are relevant for the domain framework instantiation,
the complete C++ model must be traversed. Furthermore, the order of the class instantiations
is not arbitrary because some classes need other classes directly during their construction [79].
For example, each CEVCState object needs its parent CEVCStateMachine instance to register
itself as new state. Also, for other classes, it is necessary to primary create a vector of pointers
to other already existing class instances, which are then used during the object construction.
This is the case, for example, for CDataFlow objects, which need a vector of CFunctionBlock
pointers, which defines the objects used in the data flow. Therefore, several helper methods
were implemented to separately handle the generation of different model parts and to provide
a better structured implementation. For clarification, the whole generation process is shown as
UML interaction diagram from the view of the CMain class.
In the first step, the GOPPRR C++ abstract syntax model is created by CreateSyntax-
FromFile() method of the transformation class. This creates the CGOPPRRSyntaxTree
object m_pTree, which additionally creates the underlying m_pProject with the GOPPRR
C++ abstract syntax model.
Directly afterwards, the underlying CProject instance is returned by the GetProject()
method and checked for validity according to the static semantics because the generation
process should only be executed for valid models.
CCPPGenerator Implementation The generation of the C++ source code for the openETCS
domain framework instantiation is started by the Generate() method of the m_CppGenerator
object. Initially, the GenerateRootGraph() method generates all sources for the instantiation
of the parent CEVCStateMachine object after the source file’s initial part 5 was added by the
GenerateHeader() method. This is followed by the generation of all other objects by the
related helper methods. All instantiations are generated surrounded by a main() function
block [79] in order that the source code file can be directly compiled as executable binary. Since
only valid models are used for generation, the CCPPGenerator methods do not need a special
error handling for faults related to the model. Only general faults, as segmentations, should be
handled or, even better, avoided. Thus, most of the implementation of the CCPPGenerator
methods is mostly the iteration over GOPPRR C++ abstract syntax model objects and does
not need to be discussed here in more detail or by examples.
More complicate is the generation of the execution order of function block objects, which
importance was derived and explained in Section 7.6 and Section 7.7. Simplified expressed,
function block objects should be executed in the order of the direction of the data flow. In cases
of open loops, this means starting from the objects that only have outputs. For closed loops,
the start and end object cannot be defined in a general manner if they do not have any element
5 with comments about creation time, model name, etc.
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