Automatic Resource Management Class Templates Tutorial

The LCleanedupX class provide a means of automatically cleaning up local variables on scope exit. Variants are provided for cleaning up pointers, references, handles and arrays, as well as generic cleanup items. The user is able to define a cleanup strategy to clean up the resource on scope exit.

Before beginning you must know the following:

  • Clean-up Stratergy: Cleanup strategies can be specified as an optional template parameter of the class templates for automatic resource management.

  • Declaring an LCleanedupX object

    An LCleanedupX object is declared using one of the class template constructors. The type to be managed is declared as the first template parameter. An optional second template parameter can be declared to implement a non-default cleanup strategy.

    An example code snippet for declaring LCleanedupX class is shown below:

    class LCleanedupPtr
                CTicker* ticker1 = new(ELeave) CTicker;
                LCleanedupPtr CManagedUserTwoPhase one(CManagedUserTwoPhase::NewL(ticker1));
                CTicker* ticker2 = new(ELeave) CTicker;
                LCleanedupPtr CManagedUserSinglePhase two(CManagedUserSinglePhase::NewL(ticker2));
  • Disabling Automatic Cleanup

    An object that is being managed by an LCleanedupX class can be unmanaged by calling the Unmanage() method of the LCleanedupX class.

    The managing object can be accessed using the . operator as in the call to Unmanage(). The Unmanage() disables cleanup and yields the previously managed pointer so that it can be safely returned.

    An example code snippet is given below:

            static CStringUserTwoPhase* NewL(const TDesC& aName)
                    LCleanedupPtr CStringUserTwoPhase self(new(ELeave) CStringUserTwoPhase);
                    return self.Unmanage(); 
  • Accessing the managed object

    The managed object can be accessed using the -> operator as in the call to ConstructL()

  • Passing the managed object to a function

    The managed object can be passed to a function by dereferencing the managing object. An example code snippet is given below:

    void RegisterTicker(CTicker& aTicker)

    The RegisterTicker function defined above takes a CTicker& argument. If we have a LCleanedupPtr<CTicker> as defined below, we can pass the CTicker object to the function by dereferencing as shown below in the code snippet:

    LCleanedupPtr CTicker t(new(ELeave) CTicker);
    RegisterTicker(*t); // Takes a CTicker&