smart pointer trouble
Author
I made a smart pointer (that does reference counting), and I'd like to do the following;
Suppose I have a class CFoo, and a class derived from CFoo named CBar.
I have two smart pointers; SmartPtr<CFoo> foo and SmartPtr<CBar> bar.
Suppose bar holds a valid pointer.
My (templated) smart pointer can't do this;
foo = bar
Is there any way to solve this? If so, how?
My smart pointer (cRefHandle, bottom of file) definition can be found at http://king0r.dyndns.org/svn/kbl/kbl/base/refcount.h
Any help is welcome!
A templated operator= will preserve type-safety and allow you to implicitly cast just like a regular pointer.
class Foo{};class Bar : public Foo{};class Blah{};template<class Type>class Ptr{public: template<class NewType> Ptr & operator=(Ptr<NewType> & nt) { mPtr = nt.mPtr; return *this; } Type * mPtr;};void main(){ Ptr<Foo> foo; Ptr<Bar> bar; Ptr<Blah> blah; foo = bar; //works fine foo = blah; //throws compile error system("pause");}
Author
I tried it; the compiler complains that I cannot access nt's private member mPtr (which, in my case, indeed is private). Is there a workaround for this problem?
Nearly there though... Thanks!
Nearly there though... Thanks!
I haven't tried this, but perhaps you could do something like this?
Using the friend keyword, you can allow all instances of Temp access to each others private members.
EDIT: However to preserve type safety, you should try to check to ensure that the cast is valid before you accept the pointer.
template <class T>class Temp{ friend class Temp; int m_value;public: Temp(int value) : m_value(value) { } template <class U> void Method(const Temp<U>& temp) { cout << temp.m_value << "\n"; }};Using the friend keyword, you can allow all instances of Temp access to each others private members.
EDIT: However to preserve type safety, you should try to check to ensure that the cast is valid before you accept the pointer.
Alternatively, add a...
...to your smart pointer declaration. It's not pretty, but it keeps your code safe (const-correct) and relieves you of the responsibility of making endless friend declarations.
_t * const GetPtr() const { return privateptr; }...to your smart pointer declaration. It's not pretty, but it keeps your code safe (const-correct) and relieves you of the responsibility of making endless friend declarations.
Author
I tried it; the compiler complains that there is no acceptable conversion and something about ambiguous constructors :(
I could easily hack my way out by defining the () operator ( operator T*() ) but hiding the pointer is the point (pun not intended) of a smart pointer.
I could easily hack my way out by defining the () operator ( operator T*() ) but hiding the pointer is the point (pun not intended) of a smart pointer.
Author
Quote:Original post by Tim Cowley
Alternatively, add a...
*** Source Snippet Removed ***
...to your smart pointer declaration. It's not pretty, but it keeps your code safe (const-correct) and relieves you of the responsibility of making endless friend declarations.
I can't do that; it would expose the pointer which, I want to avoid :(
EDIT: i.e. "delete smartptr.GetPtr();" would mess up my reference counting.
Author
This subject is giving me a headache...
I'm pretty sure this problem is solvable, but I decided reference counting is not the way to go for what I'm doing (a GUI... refcounting every control is kind of stupid and unnecesary). I really only need the smart pointers for recourse management - I don't even need typecasting.
Thanks for all your help! (rate++)
I'm still interested in the solution though, or some good articles about templates (I'm considering buying this book; http://www.informit.com/title/0201704315).
I'm pretty sure this problem is solvable, but I decided reference counting is not the way to go for what I'm doing (a GUI... refcounting every control is kind of stupid and unnecesary). I really only need the smart pointers for recourse management - I don't even need typecasting.
Thanks for all your help! (rate++)
I'm still interested in the solution though, or some good articles about templates (I'm considering buying this book; http://www.informit.com/title/0201704315).
Quote:Original post by Kurioes
I tried it; the compiler complains that there is no acceptable conversion and something about ambiguous constructors :(
I could easily hack my way out by defining the () operator ( operator T*() ) but hiding the pointer is the point (pun not intended) of a smart pointer.
Hmmm, Wavarian's solution worked for me. This is what you tried?
template <class _t>class cRefHandle{ friend class cRefHandle;...
Author
Yes I did. The errors were probably generated by something else (my smart pointer class contains sone other operators and member functions). You could take a look at it if you want; the URL is in my first post.
p.s. It'll probably take a while (> day) for me to reply (provided I don't forget completely).
p.s. It'll probably take a while (> day) for me to reply (provided I don't forget completely).
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