pointer to instance class containing vector<int> issue

I have a class like this:

class lar开发者_运维技巧geInt{
  vector<int> myVector;
  largeInt  operator*  (const largeInt &arg);

}

in my main i can't avoid copies while working with pointers:

void main(){

    //this works but there are multiple copies: I return a copy of the calculated
    //largeInt from the multiplication and then i create a new largeInt from that copy.
    largeInt testNum = 10;
    largeInt *pNum = new HugeInt( testNum*10);

    //i think this code avoid one copy but at the end hI points to a largeInt that has
    // myVector = 0 (seems to be a new instance = 0 ). With simple ints this works  great.
    largeInt i = 10;
    largeInt *hI;
    hI = &(i*10);

}

I think I'm missing/not managing something in vector design.. I could i achieve a copyless assigment of a pointer, even without instanciating a new largeInt? Thank you experts!

---

hI = &(i*10); takes the address of a temporary largeInt which is destructed immediately after the ';' - so hI points to invalid memory.

When you multiply two largeInt you do get a new instance - that's what multiplication does. Perhaps you intended to make an operator*= instead? That should modify an existing instance rather than creating a new.

Consider:

int L = 3, R = 5;

int j = L*R; // You *want* a new instance - L and R shouldn't change
L*=R; // You don't want a new instance - L is modified, R is unchanged

Also, you shouldn't use new to create largeInt's on heap - just do like this:

largeInt i = 10; 
largeInt hi = i*10; // Create a temporary, copy construct from the temporary

Or:

largeInt i = 10;
largeInt hi = i; // Copy construction
hi *= 10; // Modify hi directly