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;
}
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?
With built-in types, you actually have to do the initialization yourself:
class parent
{
public:
parent() : i() {}
int i;
};
This will initialize i to 0.
Built in data types (like int) are not really initialized. Their "default constructor" does nothing and they have no default value. Hence, they just get junk values. You have to explicitly initialize built in data types if you want them to have a specific value.
std::complex has a constructor that initializes its members to zero. If there isn't a constructor initializing something (or something explicitly being assigned to it), then it's going to have a junk value.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
