Question

I encountered something that I can’t understand.

I have this code:

cout << "f1 * f1 + f2 * f1 - f1 / f2 is: "<< f1 * f1 + f2 * f1 - f1 / f2 << endl;

All the “f”s are objects, and all the operators are overloaded.

The weird this is that the first computation is of the / operator,
then the second * and then the first *; after that, the operator + and at last, operator -.

So basically, the / and * worked from right to left,
and the + and - operators worked from left to right.

I made another test…
I checked this code:

 cout << "f1 * f1 / f2 is: " << f1 * f1 / f2 << endl;

Now, the first operator was * and only then operator /.
So now, it worked from left to right.

Can someone help me understand why is there difference in the directions?

10X!

Answer 1

This is yet again a question of the order of evaluation of function parameters – C++ does not specify such an order. Your code is equivalent to:

(f1 * f1) + (f2 * f1) - (f1 / f2)

The three multiply and divide operations can be evaluated in any order. This is perhaps cleraer for named functions:

add(f1*f2,f2*f1)).minus(f1/f2);

The bottom line is that associativity and precedence have nothing to say about the order of evaluation of function parameters and/or sub-expressions. Given the simple expression:

a + b

the C++ (and C) compiler is free to evaluate a first, then b, or b first then a, whether or not the ‘+’ is overloaded.