Single Phase Constructor Tutorial

Single phase construction is enabled by defining the CONSTRUCTORS_MAY_LEAVE() macro in a public section of a class definition if the single phase construction is part of the public interface of the class.

1. Enabling single phase constructor

   Single phase construction is enabled by defining the CONSTRUCTORS_MAY_LEAVE() macro in a public section of a class definition if the single phase construction is part of the public interface of the class. An example of this is given below:

           class CManagedUserSinglePhase : public CBase
   	{
   public:
   	CONSTRUCTORS_MAY_LEAVE
   	static CManagedUserSinglePhase* NewL(CTicker* aTicker)
   		{
   		return new(ELeave) CManagedUserSinglePhase(aTicker);
   		}
   	. . .
   	}
          

2. Using single phase constructor

   This macro must be used within a public section of a class definition, if the single phase construction is part of the public interface of the class. Other classes, not derived from CBase will not be affected by this macro.

   The following example code snippet the class demonstrates the use of an embedded string in the ingle-phase construction pattern, where a leave-safe constructor fully initializes the object.

           class CStringUserSinglePhase : public CBase
   	{
   public:
   		CONSTRUCTORS_MAY_LEAVE
   
   	static CStringUserSinglePhase* NewL(const TDesC& aName)
   		{
   		return new(ELeave) CStringUserSinglePhase(aName);
   		}
   
   	~CStringUserSinglePhase()
   		{
   		
   		}
          

3. Need to declare the CONSTRUCTORS_MAY_LEAVE macro

   This is necessary because the Symbian platform currently lacks the placement delete operator counterparts corresponding to the CBase placement new operators that take a TLeave parameter (new(ELeave)). The macro defines these missing placement delete operators and ensures that all allocated memory can be freed if a constructor leaves.