Question

I have simple sample:

#include <iostream>

class parent {
public:
    int i;
};

class child : public parent {
public:
    int d;
};

int main() {
    child c;
    std::cout << c.d << std::endl;
    return 0;
}

If you do not explicitly initialize a base class or member that has constructors by calling a constructor, the compiler automatically initializes the base class or member with a default constructor.

but all ints in c (int d; and int i;) are not initialized.

What is wrong with it? Or I do not see something obvios?

Answer 1

There is a difference between default and zero initialization done on classes with no constructor and basic types:

child c1;           // Default initialized. int types are not initialized.
child c2 = child(); // Zero initialized.    int types are in initialized to zero.
// In C++ 11
child c3 {};        // Use new syntax for zero initialization

More detailed explanation:
here: https://stackoverflow.com/a/7546745/14065
here: https://stackoverflow.com/a/8280207/14065