类（具有 static 成员）在 c++ 中初始化

Question

I was trying to understand friend functions and I found myself writing the following code

though I have understood the friend functions, this code leaves me with new questions:

1. how does the class initialise here when I havn't instantiaied any object

I know static member is shared by all objects of the class and is initialized to zero when the first object is created

2. at what point does the variables base_i and derived_i get assigned to respective values from code

I suppose it happens at return derived::derived_i + derived::base_i;

3. if so, does that also allocate the memory for all the other members of class at that point, specifically also for newVar in this case

#include <iostream>

class base
{
private:
    static int base_i;
    float newVar;
public:
    friend int addClasses();
};

int base::base_i = 5;

class derived : private base
{
private:
    static int derived_i;
public:
    friend int addClasses();
};

int derived::derived_i = 3;

int addClasses()
{
    return derived::derived_i + derived::base_i;
}

int main()
{
    std::cout<<addClasses()<<std::endl;
}

Answer 1

how does the class initialise here when I havn't instantiaied any object

You've initialised the variable in its definition:

 int base::base_i = 5; // <-- the initialiser

The language implementation takes care of the rest.

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at what point does the variables base_i and derived_i get assigned to respective values from code

Non-local variables with static storage duration are initialised before main is called.

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does that also allocate the memory for all the other members of class at that point, specifically also for newVar in this case

Memory for non-static member variables is "allocated" when memory for instance of the class is allocated. You didn't instantiate the class in the example program.