CODEWITHSUNDEEP
c++opencvinheritancecallback
waas1919
waas1919

Reputation: 2605

C++ OpenCV mouseCallback on inheritance class

Consider the Base class, and the two Child classes:

class Base
{
public:
    ~Base() = default;

    virtual void mouseCallback() = 0; // this is overriden by the Childs!

    void mouseCallback2() { std::cout << "mouseCallback2 OK" << std::endl; }//Not overriden
};

class Child1 : public Base
{
public:
    ~Child1() = default;

    void mouseCallback() override;
};

class Child2 : public Base
{
public:
    ~Child2() = default;

    void mouseCallback() override;
};

Where the implementation is:

void Child1::mouseCallback()
{
    std::cout << "Child 1 OK" << std::endl;
}

void Child2::mouseCallback()
{
    std::cout << "Child 2 OK" << std::endl;
}

I have my CameraVision class:

class CameraVision
{
public:
   // ...
   void init();
   static void callback(int event, int x, int y, int flags, void* userdata);
private:
   Base* mBase; // A pointer to the Base class!
}

Which contains the init() method as follows:

void CameraVision::init()
{
    mBase = new Child1();

    // Here I set the callback
    cv::setMouseCallback("Title", callback, &mBase);
}

So that when the mouse has an event I have this, the overriden method crashes my application.

void CameraVision::callback(int event, int x, int y, int flags, void* userdata)
{
    if (event == cv::EVENT_LBUTTONDOWN)
    {
        Base* tof = static_cast<Base*>(userdata);

        tof->mouseCallback2(); // THIS WORKS!

        // But this is what I need
        tof->mouseCallback(); // ERROR!!!!!!
    }

}

Why I can't use the mouseCallback() using inheritance of Child1?

I'm getting an error:

Exception thrown at 0x000000013F391938 in Demo.exe: 0xC0000005: Access violation executing location 0x000000013F391938

I was expecting the output:

mouseCallback2 OK
Child 1 OK

Upvotes: 0

Views: 68

Answers (1)

Tony J
Tony J

Reputation: 651

mBase is type Base*, then you don't need to use &, simply cv::setMouseCallback("Title", callback, mBase);

&mBase will give you a pointer to a pointer, so your static_cast doesn't give you back the original mBase pointer, but its address. Not sure how the first callback worked, both should result in UB.

Upvotes: 2

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