The genx command (at the NSCl this is in /uar/opt/genx/bin/genx) translates a structure definition file into at least a C++ header and a C++ executable. The header defines the structs and instances you've declared using the data types expected by the analysis framework you chose as the target. It also creates prototype definitions for a mimnimal set of functions for each framework. The C++ executable, contains the actual storage for your instances, any executable code needed to support the instances and implementations of the API functions.
These two files will allow you to treat the instances as structs and variables.
In this chapter we're not going to look at the generated code but rather what you need to do to generate the code.
The genx command must be given three bits of information:
--targetThe value of this option identifies which analysis framework code will be generated for (selects what's called the backend of genx). Supported values at this point in time are spectcl generates code for NSCLSpecTcl and root generates code for CERN Root.
The path to the file that contains your structure and instance definitions.
The basename for the files that will be generated. If, for example I choose a basename like spec, the header spec.h and C++ file spec.cpp will be generated.
Example 3-1. Generating SpecTcl code from data.decl
/usr/opt/genx/bin/genx --target=spectcl data.decl spec
Generates spec.h and spec.cpp.
Example 3-2. Generating CERN/Root code from data.decl
/usr/opt/genx/bin/genx --target=root data.decl root
Generates root.h, root.cpp and root-linkdef.h. root-linkdef.h is a file that allows you to build the class dictionary Root will need to use the classes and structs defined and implemented in root.{h,cpp} in interpreted Root code. More on this when we look at the generated code.
In addition to the data definitions and method implementations, three functions are declared in the header and implemented in the C++ file:
InitializePerforms one-time initialization required by the framework.
SetupEventPerforms any initialization needed before you can fill your data structures with the unpacked event.
CommitEventPerforms any actions needed by the analysis framework after the event has been unpacked.