Question

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What are access specifiers? Should I inherit with private, protected or public?

While going through the Qt API documentation, I came across protected types. What are protected types in C++?

I found an example of protected types mentioned in the QT documentation.

Answer 1

“Protected types” are nested typedefs and nested classes and templates and enums (i.e. nested types) that are protected, that is, accessible only in scope of the member functions of the class and member functions of derived classes (and friends, of course).

class A
{
    private:
        typedef int Int_Private;
    protected:
        typedef int Int_Protected;
    public:
        typedef int Int_Public; 
    void member() 
    {  
         Int_Private i1; //OK
         Int_Protected i2; //OK    
         Int_Public i3; //OK
    }
};

class B:A
{
    void derived_member()
    {
         Int_Private i1; //ERROR
         Int_Protected i2; //OK    
         Int_Public i3; //OK

    }
};

void someFunction()
{
         A::Int_Private i1; //ERROR
         A::Int_Protected i2; //ERROR    
         A::Int_Public i3; //OK
}