派生类中基类委派的ctor的c ++使用

Question

I'm taking a C++ class, and we're learning outdated C++ unfortunately. This question is specific and I couldn't just Google it. Thank you for answering.

How do I / can I access base privates from a derived ctor init-list? How do I / can I call a function from a derived ctor execution block?

point.h

class Point {
    const double x;
    const double y;
public:
    Point () = delete;
    Point ( Point && other ) : x { other.x }, y { other.y } {}
    explicit Point ( double xx, double yy) : x { xx }, y { yy }, {}

city.h

class City : public Point {
    const std::string name;
public:
    City () = delete;
    City ( City && other )
      : Point ( std::forward < City > ( other ) ) { name = other.name; }
    // is other scrapped by the time I try to get the name?
    explicit City ( double xx, double yy, std::string nname )
      : Point ( xx, yy ) { name = nname; }

( explicit ctor for ease of reference; it's the only explicit ctor I have)

In City's explicit ctor and City's move ctor , I get the same error: no overload found for operator= . Ditto with string::assign , and every other string method. What's going on? string is included.

If I stick protected: in front of Point's privates and then try to initialize them in the explicit City ctor initialization list x { xx }, .. name { nname } {} , the error says x is not a member or base class

Answer 1

The problem is that if std::string name is marked const , then you cannot assign to it, as std::basic_string<>::operator= is of course non-const. Just initialize it in the constructor list initialization like name {other.name}

Below is an example:

#include <iostream>

class Point {
    const double x;
    const double y;
public:
    Point () = delete;
    Point ( Point && other ) : x { other.x }, y { other.y } {}
    explicit Point ( double xx, double yy) : x { xx }, y { yy } {}
};
class City : public Point {
    const std::string name;
public:
    City () = delete;
    City ( City && other )
        : Point ( std::forward < City > ( other ) ) , name {other.name}{}


    // is other scrapped by the time I try to get the name?
    explicit City ( double xx, double yy, std::string nname )
        : Point ( xx, yy ), name{nname}{}
};

int main()
{
}