Sudden NULL value in C++ object

Question

Assume that I have three files: A.hpp, A.cpp, B.cpp

Here's the content of A.hpp:

#ifndef CELLML_MODULES_HPP
#define CELLML_MODULES_HPP

static Cardboard *cb1;    <--- assume Cardboard as a C++ generic class
...
int dummy_funct();

#endif

For the A.cpp:

#include "A.hpp"

int dummy_funct()
{
    cb1 = new Cardboard();
    ...
    cb1->doSomething();
}

Lastly, the B.cpp:

#include "A.hpp"

int main()
{
    ...
    dummy_funct();
    ...
    cb1->doSomething();
}

At B.cpp, cb1->doSomething got error NULL pointer, as such that the cb1 is still NULL. I've already made sure that cb1 is initialized in the dummy_funct function. Why does this happen? Is static class can be NULL even after initialization?