c++ pointer to pointer and call function that receive pointer to pointer

Question

The question is how to call function that request pointer to pointer if we are already at the function that operate with pointer to pointer . I tried some variants but all of them compile with error (SIGSEGV) http://rextester.com/ZSW68923

void test_sessiontwo ( int **ptr_to_ptr )
{
    std::cout << *ptr_to_ptr;    
}

void test_session ( int **ptr_to_ptr )
{
    std::cout << "Hello, world2!\n" << *ptr_to_ptr;    
    **ptr_to_ptr = 20;
     test_sessiontwo   ( ptr_to_ptr ); // ERROR. HOW TO CALL THIS???
}

int main()
{
    int* ptr_int;
    *ptr_int = 10;
    test_session ( &ptr_int );   

    std::cout << "Hello, world!\n";
}

Answer 1

This code segment

   int* ptr_int;
    *ptr_int = 10;

is already wrong. Pointer ptr_int was not initialized. So the program has undefined behaviour.

To test your code you could write for example

int main()
{
    int* ptr_int = new int( 10 );
    test_session ( &ptr_int );   

    std::cout << "Hello, world!\n";

    delete ptr_int;
}

Answer 2

Try

int i=10;
int *ptr_int = &i;
test_session(&ptr_int);