Question

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Trouble with inheritance of operator= in C++

I updated the code

#include <QtCore/QCoreApplication>

class Base
{
    int num;
public:
    Base& operator=(int rhs)
    {
        this->num = rhs;
        return *this;
    }
};

class Derive : public Base
{
public:
    int deriveNum;
    using Base::operator =; // unhide the function
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    Base base;
    Derive derive1, derive2;

    base = 1;  // calls Base::operator(1) and returns Base&

    derive1 = 11; // calls Base::operator(11) and returns Base&
    derive2 = 22; // calls Base::operator(22) and returns Base&

    derive1 = base;// Which function does it calls??
               // If it calls Base::operator(base) and
                   // returns a Base&, how could it be assigend to derive1?

    return a.exec();
}

I marked the question in the comment, please give me some more help

Answer 1

It is inherited by the derived class. However, the derived class has it own operator = (implictly declared by the compiler), which hides the operator = inherited from the parent class (search and read about “name hiding” in C++).

If you want the inherited operator = to become visible, you have to explicitly unhide it

class Derive : public Base
{
  std::string str;

public:
  using Base::operator =; // unhide
};

and your code will compile. (If you fix the obvious syntax errors that is. Please, post real code.)

P.S. This question is asked very often. I provided a link to a more detailed explanation as a comment to your question.