Is this copy constructor elision?

Question

The following code doesn't call the copy constructor.

struct X
{
   int x;
   X(int num)
   {
      x = num;
      std::cout << "ctor" << std::endl;
   }
   X(const X& other)
   {
      std::cout << "copy ctor" << std::endl;
   }
};

int main(int argc, _TCHAR* argv[])
{
   X* x = new X(3);
   X* y(x);
}

Output:

ctor

Is it copy-ctor elision?

I can't see a single copy that even could be elided. Are you sure your example is correct? — CB Bailey, May 15 '12 at 07:09
@CharlesBailey well `X(const X& other)` **could** be elided in the right context (which this isn't). — Luchian Grigore, May 15 '12 at 07:21
Please don't learn C++ with a Java book, it doesn't do anybody any good. — Christian Rau, May 15 '12 at 07:42
@LuchianGrigore: I don't believe there's a single copy of `X` being made in the whole example - candidate for elision or not. Have I missed something? — CB Bailey, May 15 '12 at 08:29

score 9 · Accepted Answer · answered May 15 '12 at 06:53

9

The code

X* x = new X(3);
X* y(x);

is not the same as

X x(3);
X* y = new X(x);

You're not copying objects, but pointers. After X* y(x);, both pointers will point to the same object.

answered May 15 '12 at 06:53

Luchian Grigore

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Is this copy constructor elision?

1 Answers1