Why does this allow promotion from (char *) to (const char *)?

Question

Given that scanf has (const char *) in the documentation from Microsoft and the answer to this question what the heck is going when I do the same for (char **) promotion to

Answer 1

Check if this clarifies for you:

char * a_mutable = /*...*/;
const char * a_constant = /*...*/;

char **pointer_to_mutable = &a_mutable;   /* ok */

const char **pointer_to_constant = &a_constant;   /* ok */

pointer_to_constant = pointer_to_mutable;   /* oops, are you sure? */

*pointer_to_constant = a_mutable;   /* valid, but will screw things around */

The last line is valid, since pointer_to_constant is a mutable pointer to a mutable pointer to a constant character, but it would break things since you are making a_constant point to a_mutable. That is why you are not allowed to make pointer_to_constant receive the contents of pointer_to_mutable.