In the code below I have one UserInterface shared_ptr obj, but when the program finished its destructor is called multiple times as in the output below:

finishing...
Destroying UserInterface
Destroying InterfaceElement Submit button
Destroying UserInterface
Destroying InterfaceElement Spouse's name textbox
Destroying UserInterface
Destroying InterfaceElement Is married checkbox
Destroying UserInterface
Destroying InterfaceElement Name textbox
Destroying UserInterface
free(): double free detected in tcache 2
Aborted

I was expecting the “Destroying UserInterface” message to be displayed only once since I only got the ui reference. Why does this happen?

    #include <iostream>
#include <memory>

using std::string, std::shared_ptr, std::cout, std::unique_ptr;

class Mediator {
public:
    virtual void mediate(const string& event) = 0;
};
typedef shared_ptr<Mediator> mptr;

class InterfaceElement {
protected:
    mptr mediator;
    string name;
    bool isVisible = true;
public:
    InterfaceElement(const string& name, bool isVisible, mptr mediator) : name(name), isVisible(isVisible), mediator(mediator) {};

    ~InterfaceElement(){
        cout << "Destroying InterfaceElement " << name << "n";
    }
};

class ButtonElement : public InterfaceElement {
    // similar to class CheckBox
};

class TextBox : public InterfaceElement {
    // similar to class CheckBox

};

class CheckBox : public InterfaceElement {
    bool isChecked = false;
public:
    CheckBox(const string& name, bool isVisible, mptr mediator) : InterfaceElement(name, isVisible, mediator) {};
    virtual ~CheckBox() {};
    virtual void setIsChecked(bool isChecked) {
        this->isChecked = isChecked;
        
        if (isChecked) {
            mediator->mediate(name + " is checked");
        } else {
            mediator->mediate(name + " is unchecked");
        }
    };
};

class UserInterface : public Mediator {
    shared_ptr<TextBox> nameTextBox;
    shared_ptr<CheckBox> isMarriedCheckbox;
    shared_ptr<TextBox> spousesNameTextBox;
    shared_ptr<ButtonElement> submitButton;
public:
    UserInterface() {
        nameTextBox = shared_ptr<TextBox>(new TextBox("Name textbox", true, shared_ptr<Mediator>(this)));
        isMarriedCheckbox = shared_ptr<CheckBox>(new CheckBox("Is married checkbox", true, shared_ptr<Mediator>(this)));
        spousesNameTextBox = shared_ptr<TextBox>(new TextBox("Spouse's name textbox", false, shared_ptr<Mediator>(this)));
        submitButton = shared_ptr<ButtonElement>(new ButtonElement("Submit button", false, shared_ptr<Mediator>(this)));
    }
    ~UserInterface() {
        cout << "Destroying UserInterfacen";
    }
    void mediate(const string& event) override {
        cout << "Mediating event: " << event << "...n";
        
    }
    shared_ptr<TextBox> getNameTextBox() { return nameTextBox; };
    shared_ptr<CheckBox> getIsMarriedCheckbox() { return isMarriedCheckbox; };
    shared_ptr<TextBox> getSpousesNameTextBox() { return spousesNameTextBox; };
    shared_ptr<ButtonElement> getSubmitButton() { return submitButton; };
};
typedef unique_ptr<UserInterface> uiptr;

int main(int argc, const char * argv[]) {
    uiptr ui = uiptr(new UserInterface);


    cout << "finishing...n";
    return 0;
}