Member initializer list in derived class

Question

#include <iostream>

#define Log(x) std::cout << x << std::endl;

class A {
public:
int c;
//A():c(5){};
};

class B : public A {
public:
B() :c(12) {};
};
int main()
{

B x;
Log(x.c);

}

//So the question is why can't you initialize derived members in the sub class.

Answer 1

Well, it seems the member initializer list is only for the members of the class to be initzialized. The base class is either initizialized automatically or you do a :A(). And that's also the way to initialize members of A differently in B:
#include <iostream>
using namespace std;

#include <iostream>

#define Log(x) std::cout << x << std::endl;

class A {
public:
int c;
A(int a = 5):c(a){};
};

class B : public A {
public:
B() : A(12) {};
};

int main()
{

B x;
Log(x.c);

}

Answer 2

BTW: Do you know RAII: Resouce Acquisition Is Initializiation. So all members of a (base) shall be initialized after construction.

Answer 3

This was bugging me for a while, thanks for answering this.No, I don't know about RAII. If you would explain it a bit more I would love to learn about it. Thanks for the answer.

Answer 4

wikipedia has a good explanation. Or cppreference.com. they can explain better than i do.