C++ overloading operators

Question

I'm stuck with overloading operators "+", "-", "/" and "*" in my program. Basically I've got an object, which is dynamically allocated array of double values. I've got the whole program, but I can't get through those overloads.

my constructor looks like this:

table::table(int size) {
    this->size = size;
    tab = new double[size];
    count++;
}

I've wrote something like that:

table & table::operator-(const table &tab3 )
{
        table * tab_oper2 = new table(size);
        for(int i=0; i< tab3.size; i++) 
        {
            (*this).tab[i] -= tab3.tab[i];
        }
        return *this;
}

which generally works, but It's not generally good way to do it. My instructor told me to try to switch (*this) to *tab_oper2, return it as a reference but it doesn't work. Please, could someone tell me how to do it properly?

Answer 1

C++ is a value oriented language; return a table (and not a table& ). Construct the return value in a local variable, and return it. And don't forget the rule of three: given the little code you've shown, you'll need a copy constructor, an assignment operator and a destructor. (Of course, if you use std::vector , rather than new[] , all of this will be taken care of for you.)

Answer 2

You should return a third object result by value:

table table::operator-(const table &t) const
{
        table result(size);
        for(int i=0; i< t.size; i++) 
        {
            result.tab[i] = this->tab[i] - t.tab[i];
        }
        return result;
}

operator - is different from operator -= which you was writing. When you're overloading operator- you shouldn't manipulate this .

Answer 3

You are allocating a result table but you are not populating it. Populate the result table and it will work.

table & table::operator-(const table &tab3 )
{
        table * tab_oper2 = new table(size);
        for(int i=0; i< tab3.size; i++) 
        {
            tab_oper2->tab[i] = tab[i] - tab3.tab[i];
        }
        return *tab_oper2;
}