CODEWITHSUNDEEP
c++pointersshared-ptr
Michael Afonso
Michael Afonso

Reputation: 23

how can you see if shared pointers are equal to each other

i'm trying to implement a Flyweight design in c++. This is what I have so far.

std::unordered_map<std::pair<Gdiplus::Color, float>, std::shared_ptr<Gdiplus::Pen>> mymap;
std::shared_ptr<Gdiplus::Pen> getPen(Gdiplus::Color const & color, float width )
{   
    std::pair<Gdiplus::Color,float> input;
    input = std::make_pair(color, width);
    std::unordered_map<std::pair<Gdiplus::Color, float>, std::shared_ptr<Gdiplus::Pen>>::const_iterator got = mymap.find (input);

        if ( got == mymap.end() )
        {
            auto pen = std::make_shared<Gdiplus::Pen> ();
            pen->SetColor(color);
            pen->SetWidth(width);
            //std::pair<Gdiplus::Color,float> input2;
            mymap.insert(std::make_pair(input, pen));
            return pen;             
        }       
        else
        {
            if (std::shared_ptr<Gdiplus::Pen> m_pen = got->second.get())
               return m_Pen;
        }

}

My issue is in the else statement. i'm trying to figure out if both pointers are the same but i get an error saying 

cannot convert from 'Gdiplus::Pen *' to 'std::tr1::shared_ptr<_Ty>'

Upvotes: 1

Views: 129

Answers (1)

Tushar
Tushar

Reputation: 8049

Your problem lines in this line:

std::shared_ptr<Gdiplus::Pen> m_pen = got->second.get();

Explanation:

std::shared_ptr<T>.get() returns the internal pointer stored by a shared_ptr (i.e., Grdiplus::Pen*). Try this instead:

std::shared_ptr<Gdiplus::Pen> m_pen = got->second;

This will allow you to assign to m_pen, since there is no implicit conversion from T* to std::shared_ptr<T>.

Upvotes: 2

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