Singleton classes

Many resource classes, such as IccFile, can be used to create multiple resource objects within a single program. However, some resource classes are designed to allow the programmer to create only one instance of the class; these are called singleton classes. Any attempt to create more than one object of a singleton class results in an error; a C++ exception is thrown.

The following Foundation Classes are singleton:
  • IccAbendData provides information about task abends.
  • IccConsole, or a derived class, represents the system console for operator messages.
  • IccControl, or a derived class, such as IccUserControl, controls the executing program.
  • IccStartRequestQ, or a derived class, allows the application program to start CICS® transactions (tasks) asynchronously.
  • IccSystem, or a derived class, is the application view of the CICS system in which it is running.
  • IccTask, or a derived class, represents the CICS task under which the executing program is running.
  • IccTerminal, or a derived class, represents your task's terminal, provided that your principal facility is a 3270 terminal.
A class method, instance, is provided for each of these singleton classes, which returns a pointer to the requested object and creates one if it does not already exist. For example: 
IccControl* pControl = IccControl::instance();