this pointer of a static object

Question

If I take this in an static object and store it in a vector in a Singleton object, can I assume the pointer points to the object during the whole lifetime of the program?

Answer 1

In general, you can't assume that, because order of static object creation in different translation units is unspecified. In this case it will work, because there is only single translation unit:

#include <iostream>
#include <vector>
class A
{
    A() = default;
    A(int x) : test(x) {}
    A * const get_this(void) {return this;}
    static A staticA;
public:
    static A * const get_static_this(void) {return staticA.get_this();}
    int test;
};

A A::staticA(100);

class Singleton
{
    Singleton(A * const ptr) {ptrs_.push_back(ptr);}
    std::vector<A*> ptrs_;
public:
    static Singleton& getSingleton() {static Singleton singleton(A::get_static_this()); return singleton;}
    void print_vec() {for(auto x : ptrs_) std::cout << x->test << std::endl;}
};

int main()
{
    std::cout << "Singleton contains: ";
    Singleton::getSingleton().print_vec();

    return 0;
}

Output:

Singleton contains: 100

But what if A::staticA in defined in different translation unit? Will it be created before static Singleton is created? You can't be sure.