Conversion of pointer-to-pointer between derived and base classes?

Regarding the following C++ program:

class Base { };

class Child : public Base { };

int main()
{   
    // Normal: using child as base is allowed
    Child *c = new Child();
    Base *b = c;

    // Double pointers: apparently can't use Child** as Base**
    Child **cc = &c;
    Base **bb = cc;

    return 0;
}

GCC produces the following error on the last assignment statement:

error: invalid conversion from ‘Child**’ to ‘Base**’

My question is in two parts:

1. Why is there no implicit conversion from Child** to Base**?
2. I can make this example work with a C-style cast or a reinterpret_cast. Using these casts means throwing away all type safety. Is there anything I can add to the class definitions to make these pointers cast implicitly, or at least phrase the conversion in a way that allows me to use static_cast instead?

Solution 1:

If this was allowed, you could write this:

*bb = new Base;

And c would end up pointing to an instance of Base. Bad.

Solution 2:

Pointers are virtual address. Normally you are responsible for what you do with it. Using msvc 2019. I can cast one to base, but not two:

example 1:

int p;
int *p1 = &p;
int **p2 = &p1; //OK

example 2:

struct xx {};
struct yy : public xx {};

yy p;
yy *p1 = &p;
xx **p2 = &p1; //Just a strange error

example 3:

struct xx {};
struct yy : public xx {};

yy p;
xx *p1 = &p; 
xx **p2 = &p1; //OK