non-const pointer argument to a const double pointer parameter

Question

The const modifier in C++ before star means that using this pointer the value pointed at cannot be changed, while the pointer itself can be made to point someth

Answer 1

As most times, the compiler is right and intuition wrong. The problem is that if that particular assignment was allowed you could break const-correctness in your program:

const int constant = 10;
int *modifier = 0;
const int ** const_breaker = &modifier; // [*] this is equivalent to your code

*const_breaker = & constant;   // no problem, const_breaker points to
                               // pointer to a constant integer, but...
                               // we are actually doing: modifer = &constant!!!
*modifier = 5;                 // ouch!! we are modifying a constant!!!

The line marked with [*] is the culprit for that violation, and is disallowed for that particular reason. The language allows adding const to the last level but not the first:

int * const * correct = &modifier; // ok, this does not break correctness of the code