Two smartpointer designs

Discussion in 'C++' started by paalkrebs@hotmail.com, Dec 1, 2007.

  1. Guest

    I've made two smartpointers that I'd like to share. Improvements and
    comments are welcome.

    The key to both is that there should be no access to the managed
    object, and all operations should be done on the smartpointers. Both
    are designed in a similar way, where a userclass inherits from a
    template and the smartpointer is defined as an internal class of the
    template;

    The first one is an automatic refcount smartpointer where the object
    pointed to keeps track of the current refcount, and the object gets
    destroyed if the refcount goes to 0. All refcount management is
    automatic.

    The second is called a safepointer, and the managed object will
    automatically clear all safepointers which references it when
    destroyed. Destruction is done through a smartpointer's destroy
    function.



    I'm including a testfile which shows how they are used, followed by
    the 2 template files:


    // ConsoleTests.cpp : Defines the entry point for the console
    application.
    //

    #include "stdafx.h"
    #include "../../common/autorefcount.h"
    #include "../../common/safepointer.h"

    class A;
    class A : public TAutoRefable<A*>
    {
    public:
    static ARPtr Create(int x){return ARPtr(new A(x));} // create an
    instance of A

    int GetX(){return mX;}
    private:
    A(int x) : mX(x){} // keep constructors private in inherited classes,
    and use Create to instanciate

    int mX;
    };

    void TestAutoRefPointer(){
    A::ARPtr c;
    bool valid = c.IsValid(); // false

    c = A::Create(1);
    if (c.IsValid()) { // true
    int x = c->GetX();
    }

    DWORD refcount = c.GetRefCount();// refcount = 1

    {
    A::ARPtr d(c);
    refcount = c.GetRefCount();// refcount = 2
    {
    A::ARPtr e;
    e = c;
    refcount = c.GetRefCount();// refcount = 3
    }
    refcount = c.GetRefCount();// refcount = 2
    }
    refcount = c.GetRefCount();// refcount = 1

    valid = c.IsValid(); // true
    c.Clear(); // refcount = 0, object gets destroyed
    refcount = c.GetRefCount();// refcount = 0
    valid = c.IsValid(); // false

    }


    class S;
    class S : public TSafeObj<S*>
    {
    public:
    static SPtr Create(int x){return SPtr(new S(x));} // create an
    instance of S
    int GetX(){return mX;}

    private:
    S(int x) : TSafeObj<S*>(5), mX(x){}// keep constructors private in
    inherited classes, and use Create to instanciate
    int mX;
    };


    void TestSafePointer(){
    S::SPtr c;

    bool valid = c.IsValid(); // false

    c = S::Create(1);
    if (c.IsValid()){ // true
    int x = c->GetX();
    }

    S::SPtr d(c);
    S::SPtr e;
    e = c;

    d.Destroy(); // destroys object, and clears all SafePointers to it


    if (c.IsValid() || d.IsValid() || e.IsValid()) {// false
    int x = c->GetX();
    }
    }


    int _tmain(int argc, _TCHAR* argv[])
    {
    TestAutoRefPointer();
    TestSafePointer();
    return 0;
    }


    // autorefcount - ptr with auto refcount

    #pragma once
    #include "comdef.h"


    template <class T> class TAutoRefable
    {
    public:
    class ARPtr
    {
    public:
    ARPtr() : mPtr(NULL){}
    ARPtr(T p) : mPtr(p) {
    if (p) {
    p->AddRef();
    }
    }
    ARPtr(const ARPtr& s) : mPtr(s.mPtr){
    if (mPtr) {
    mPtr->AddRef();
    }
    }
    ~ARPtr()
    {
    if (mPtr){
    mPtr->SubRef();
    }
    }
    DWORD GetRefCount(){return (mPtr) ? mPtr->mRefCount : 0;}

    T operator -> (){return mPtr;}
    ARPtr& operator =(const ARPtr& that){
    if (this != &that) {
    if (mPtr){
    mPtr->SubRef(); // deletes object if refcount goes to 0, so mPtr
    can point to freed mem after this.
    }
    if (that.mPtr) {
    that.mPtr->AddRef();
    }
    mPtr = that.mPtr;
    }
    return *this;
    }

    void Clear(){
    if (mPtr){
    mPtr->SubRef();
    }
    mPtr = NULL;
    }

    bool IsValid(){return mPtr != NULL;}

    private:
    T mPtr;
    };

    // initial values for event and subsciber dynamic arrays
    static ARPtr Create(){return ARPtr(NULL);} // override this with more
    interesting actions
    protected: // keep constructors and destructors protected/private in
    inherited classes
    TAutoRefable() : mRefCount(0){}
    virtual ~TAutoRefable(){}

    private:
    friend ARPtr;
    void AddRef(){mRefCount++;}
    void SubRef(){--mRefCount; if (mRefCount == 0) delete this;}

    DWORD mRefCount;
    };


    // SafePtr - clears all safeptrs when object is destroyed

    #pragma once
    #include "comdef.h"
    #include "objectarray.h"

    template <class T> class TSafeObj
    {
    public:
    class SPtr
    {
    public:

    SPtr() : mPtr(NULL){}
    SPtr(T p) : mPtr(p) {if (mPtr) mPtr->AddSPtr(this);}
    SPtr(const SPtr& s) : mPtr(s.mPtr){
    if (mPtr) mPtr->AddSPtr(this);
    }
    ~SPtr(){if (mPtr) mPtr->RemoveSPtr(this);}

    void Destroy(){
    if (mPtr){
    mPtr->RemoveSPtr(this);
    delete mPtr; // mPtr clears out other sptrs
    mPtr = NULL;
    }
    }


    T operator -> (){return mPtr;}
    SPtr& operator =(const SPtr& that){
    if (this != &that) {
    if (mPtr) mPtr->RemoveSPtr(this);
    if (that.mPtr) that.mPtr->AddSPtr(this);
    mPtr = that.mPtr;
    }
    return *this;
    }

    void Clear(){
    if (mPtr) mPtr->RemoveSPtr(this);
    mPtr = NULL;
    }

    bool IsValid(){return mPtr != NULL;}

    private:
    friend TSafeObj;
    T mPtr;

    };

    static SPtr Create(){return SPtr(NULL);} // override with more useful
    actions

    protected: // keep destructor and constructor protected/private in
    inherited classes
    friend SPtr;

    TSafeObj(DWORD ptrCount) : mSafePtrs(ptrCount){} // set up initial
    pointercount

    virtual ~TSafeObj(){
    for (DWORD i = 0; i < mSafePtrs.Size(); ++i) mSafePtrs->mPtr =
    NULL;
    }
    private:
    typedef TObjectArray<SPtr*> SafePtrArray;

    void AddSPtr(SPtr* sptr){mSafePtrs.Add(sptr);}
    void RemoveSPtr(SPtr* sptr){mSafePtrs.RemoveObj(sptr);}

    SafePtrArray mSafePtrs; // Sptrs to this object
    };
     
    , Dec 1, 2007
    #1
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