When dose the CDO object created?

[anonymous_user_ec4e83c9]

I know when a class derived from UObject,at the same time a UClass will be defined for represent the class. In the UClass,it has a property named ClassDefaultObject which is a static object of the class derived form UObject. But when dose the static Object created? This confused me very long.
In the ue4’s C++ gameplay programing frame,I found this static object is used in many ways.So who is responsible for creating this static object?
I try to write a C++ test code like this:

class A {
public:
	A(int i = 10) :m(i){}
	static A a;
	~A(){}
	int get()const
	{
		return m;
	}
private:
	int m;
};
A A::a = A();

In standard C++ code,this form is ok. So,I guess the ue4’s class static object may be also use this form.
Can someone offer me a clear explanation?