C++, Need Reason for error : cannot convert parameter 1 from 'char *' to 'const char *&'

Question

Whey we cannot Convert pointer to a character ->TO-> a reference to a pointer to a constant character

I am interested in knowing the reason of syntax error when we

Answer 1

Suppose you had

void foo_ptr(const char * & ptr)
{         
    ptr = "readonlystring";
}        

You now call it as

    char *ptr;
    foo_ptr(ptr);
    *ptr = 0;

Suppose no error were raised. You are writing to a read-only string, violating the type system without any casts.

This is basically the CV version of How come a pointer to a derived class cannot be passed to a function expecting a reference to a pointer to the base class?.