Why is the member value of parent lost in the vector after push

I would like to push an instance of Child (Parent is the base class of Child), in a vector using push_back(). But then the value of the Parent members lost. In the following example, I would like to see 70 when writing the vector to the console, but I get random value instead. What is causing this?

main.cpp:

void demo(vector<Child> &ch) {
Child c(4);
c.setPrice(70);
cout << c.getPrice() << endl; // 70
ch.push_back(c);
cout << ch[ch.size()-1].getPrice() << endl;  // random value
}
int main()
{
 vector<Child> ch;
 demo(ch);
 return 0;
}

Child.h:

#ifndef CHILD_H_INCLUDED
#define CHILD_H_INCLUDED
#include "Parent.h"
class Child : public Parent
{
private:
    int siz;
public:
    Child();
    ~Child();

    Child(int);
    Child(const Child&);

    int getSiz() const;

    void setSiz(int);
};


#endif // CHILD_H_INCLUDED

Child.cpp:

#include "Child.h"

Child::Child()
{
}

Child::Child(int siz)
{
    this->siz = siz;
}

Child::Child(const Child& other)
{
    siz = other.siz;
}

Child::~Child () {

}

int Child::getSiz() const
{
    return siz;
}

void Child::setSiz(int s)
{
    siz = s;
}

Parent.h:

#ifndef PARENT_H_INCLUDED
#define PARENT_H_INCLUDED
class Parent
{
private:
    int price;
public:
    Parent();
    ~Parent();

    Parent(int);
    Parent(const Parent&);

    int getPrice() const;

    void setPrice(int);
};

#endif // PARENT_H_INCLUDED

Parent.cpp:

#include "Parent.h"

Parent::Parent()
{
}

Parent::Parent(int price)
{
    this->price = price;
}

Parent::Parent(const Parent& other)
{
    price = other.price;
}

Parent::~Parent () {

}

int Parent::getPrice() const
{
    return price;
}

void Parent::setPrice(int p)
{
    price = p;
}

Thank you very much in advance for your help!

CodePudding user response：

The child's copy constructor only copies the child parts. It should also invoke the parent's copy constructor to let it copy the parent members.

Child::Child(const Child& other) : Parent(other)
{
    siz = other.siz;
}