Returning a reference to a local/temprorary object without causing a memory leak?

Question

I realize this is wrong (my compiler says so!):

Rectangle& Rectangle::Overlap(const Rectangle& rectangle) {

    Point topLeft(__max(this->GetVerticies()[0]->GetX(), rectangle.GetVerticies()[0]->GetX()) - __min(this->GetVerticies()[0]->GetX() + this->GetWidth(), rectangle.GetVerticies()[0]->GetX() + rectangle.GetWidth()), 
                 (__max(this->GetVerticies()[0]->GetY(), rectangle.GetVerticies()[0]->GetY()) - __min(this->GetVerticies()[0]->GetY() + this->GetHeight(), rectangle.GetVerticies()[0]->GetY() + rectangle.GetHeight())));

    Point bottomRight(__min(this->GetVerticies()[0]->GetX() + this->GetWidth(), rectangle.GetVerticies()[0]->GetX() + rectangle.GetWidth()), topLeft.GetY() + __max(this->GetVerticies()[0]->GetY() + this->GetHeight(), rectangle.GetVerticies()[0]->GetY() + rectangle.GetHeight()));

    return Rectangle(topLeft, bottomRight);
}

What would be the correct way to return the calculated rectangle without causing a memory leak? Defining the rectangle as Rectangle* result = new Rectangle(topLeft, bottomRight) then returning the dereferenced pointer works but just seems...wrong. Any suggestions?

This isn't a memory leak. On the contrary, you are freeing memory (a temporary variable that is created when you call Rectangle() constructor) before you ever get a chance to actually access it. See hkasier's answer for workarounds. — Sergei Tachenov, Dec 17 '10 at 06:25

score 4 · Accepted Answer · answered Dec 17 '10 at 01:24

4

Either return by value:

Rectangle Rectangle::Overlap(const Rectangle& rectangle);

which does not require to change your function body, or add an additional parameter to return the result:

void Rectangle::Overlap(const Rectangle& rectangle, Rectangle& out);

and assign the result to the out parameter.

answered Dec 17 '10 at 01:24

hkaiser

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Or do it the C way using a pointer in the second example. Sometimes it improves readability. – Sergei Tachenov Dec 17 '10 at 06:27

score 3 · Answer 2 · edited Jun 24 '11 at 21:26

3

Make the return type a non-reference (value). Then the returned value will be fine, using the implicit copy-constructor...

edited Jun 24 '11 at 21:26

Peter Mortensen

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answered Dec 17 '10 at 01:23

ianmac45

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score 3 · Answer 3 · answered Dec 17 '10 at 01:23

3

Just change the return type to Rectangle (sans the reference).

answered Dec 17 '10 at 01:23

Tony Delroy

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score 3 · Answer 4 · answered Dec 17 '10 at 01:24

3

Just return a Rectangle instead of a reference to one.

answered Dec 17 '10 at 01:24

Anon.

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Returning a reference to a local/temprorary object without causing a memory leak?

4 Answers4