A Simple Smart Pointer

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Here is another smart pointer implementation. It's as easy as it gets.

How to use it

#include "/libs/idlsoft/smartptr.h"
using namespace idllib;
// in a body
    SmartPtr<CMyObject> ptr1(new CMyObject);  // construct from a pointer
    SmartPtr<CMyObject> ptr2(ptr1);   // construct from a smart pointer
    SmartPtr<CMyObject> ptr3;         // construct an empty one
    ptr3 = new CMyObject;                   // assign a pointer
    ptr1 = ptr3;                            // assign a smart pointer
    ptr1->method1();                     // call a method
    ptr2 = NULL;
    // etc ...    
// in a function call
    void f(CMyObject *ob);                   // function declaration
    ...
    SmartPtr<CMyObject> ptr1(new CMyObject);
    f(ptr1);                                // function call
// as a return value
    SmartPtr<CMyObject> f1()
    {
        return SmartPtr<CMyObject>(new CMyObject);
    }
    ...
    SmartPtr<CMyObject> ptr;
    ptr = f1();

That's it!

No need to worry about freeing the pointer, the object is deleted through a standard reference-counting mechanism.

SmartPtr is the only class you really need here. It can point to anything that was allocated by the new operator.

How NOT to use it

    // 1.
    SmartPtr<CMyObject> ptr;
    CMyObject ob;
    ptr = &ob;  // DON'T ! only memory allocated by new operator should be used
    // 2.
    SmartPtr<CMyObject> ptr1, ptr2;
    CMyObject *o2 = new CMyObject;
    ptr1 = o2;
    ptr2 = o2;  // DON'T ! unless CMyObject implements IRefCount
                // try to use ptr1 = ptr2 instead, it's always safe;

How it is implemented

SmartPtr holds a pointer to a reference counting object. Every time we assign a value to SmartPtr it decrements the reference count on the current object and increments it for the new one. The reference counter for its part would delete the allocated object if the reference drops to zero.

The reference counter can be either part of the allocated object (when we implement IRefCount) or a separate object (SmartPtr::__RefCounter) that holds a pointer to it.

See next section for details.

How to optimize memory usage

In order to count references to the allocated object SmartPtr creates a special object, which means two memory allocations instead of one. If you want to optimize the memory usage just implement IRefCount in your class. You can do it yourself or use IRefCountImpl:

    class CMyObject : public CObject, public IRefCountImpl<CMyObject> {
    ...
    };

In this case SmartPtr will use the built-in counter instead of a sparate one.