C ++如何将指针向量（双指针）作为常量传递给函数

Question

I have a class A in C++ with many attributes:

 class A{
   public:
      B** tab;// B is another class or structure
      ....
      void compute();//this function does calculations on elements inside tab
   };

In a third class C , there is a function that uses the tab variable as input, reads each element and does some calculations to write results on another attribute of the class C :

C::compute(B** tab){
     ....// I need that **tab be protected inside this function and its elements does not change
 }

How can I make tab : the vector of pointers protected (or constant) ?

Answer 1

One possible way is something like this:

C::compute(B * const * tab){
   // nothing in this array of pointers will be changed
   tab[0] = (B *) 0x3254; // compile error as desired
}

Or you can ban changing even pointer to pointers like this:

C::compute(B * const * const tab){
   // nothing in this array of pointers will be changed
   tab = (B * const *) 0x3254; // compile error
}

If you need to protect only pointers in array the first example is your choice

Answer 2

How about using vector :

class A {
    vector<vector<B> > tab;
    //...
}

C::compute(const vector<vector<B> >& tab) {
    // tab, tab[0] and tab[0][0] are all const
}