CODEWITHSUNDEEP
c++constructoroperators
justAnotherUser
justAnotherUser

Reputation: 91

Some basic questions about constructor and operators

Sorry if this question sounds too basic, but I'd like to know what EXACTLY happens in this code (Point3d is my own implementation):

int main()
{
    Point3d a(1,2,3);
    Point3d b(11,12,13);
    Point3d c = a+b;
    Point3d d = a;
    Point3d e;

    return 0;
}

So after running the code above, functions are called in the following order:

Point3d (const float x, const float y, const float z) // a
Point3d (const float x, const float y, const float z) // b
Point3d () //since I created a new object in operator+
operator+ (const Point3d& rhs) //a+b
Point3d (const Point3d& rhs) //the copy constructor for d = a
Point3d () //e

I noticed something:

  1. no constructor is called for c
  2. operator= is never called (However, if I put the assignment and instance declaration in different lines, operator= is called)

Is what I observed above expected? If so, why is operator= never called?

P.S. my operator+ is returning an object rather than an reference (Point3d rather than Point3d&), I think that's correct?

Upvotes: 0

Views: 49

Answers (2)

Mari
Mari

Reputation: 9

So there's a difference between a copy constructor and an assignment operator. Instances in which you call copy constructor:

object a = b

Instances in which you call an assignment operator:

object a;
object b;
a = b;

Upvotes: 0

Remy Lebeau
Remy Lebeau

Reputation: 598174

  1. no constructor is called for c

Most likely due to Return Value Optimization.

  1. operator= is never called

Because none of the lines shown are performing assignments, only constructions. Use of = in a line that declares and assigns an object in the same statement is just "syntax sugar" for copy construction.

Point3d c = a+b; // aka: Point3d c(a+b);
Point3d d = a;   // aka: Point3d d(a);

However, if I put the assignment and instance declaration in different lines, operator= is called

Yes, if separate statements (not lines) are used for declaration and assignment, then operator= is used.

Upvotes: 3

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