Reference to AcGeCircArc2d

[karl.sch1983]

Hi friends, how can I get a reference to the center of AcGeCircArc2d. Am I approaching this incorrectly? Maybe I need to call geCir1.center() everytime? 

static void Test() {
		AcGeCircArc2d geCir1(AcGePoint2d(1, 1), 5);
		AcGePoint2d &geCtr1 = geCir1.center();
		acutPrintf(_T("\ngeCir1 Center is x: %f\ty: %f"), geCir1.center().x, geCir1.center().y);
		acutPrintf(_T("\ngeCtr1 Center is x: %f\ty: %f"), geCtr1.x, geCtr1.y);

		geCir1.setCenter(AcGePoint2d(5, 6));
		acutPrintf(_T("\ngeCir1 Center is x: %f\ty: %f"), geCir1.center().x, geCir1.center().y);
		acutPrintf(_T("\ngeCtr1 Center is x: %f\ty: %f"), geCtr1.x, geCtr1.y);
	}

Output:

geCir1 Center is x: 1.000000 y: 1.000000

geCtr1 Center is x: 1.000000 y: 1.000000

geCir1 Center is x: 5.000000 y: 6.000000

geCtr1 Center is x: 1.000000 y: 1.000000

Thanks in advance for your time.

[zrobert]

Hi;

I may be completely wrong (I'm not a c ++ expert) but in a hurry, I think the reason is that the center () method is not declared as a reference type, but as a constant value type of AcGePoint2d. (GE_DLLEXPIMPORT AcGePoint2d center () const;). So, I think you have to call geCir1.center () all the way.

[zrobert · Accepted solution]

Here is an example of declaring and defining a reference-type function, which would behave as you would like.

Example 

[Alexander.Rivilis · Accepted solution]

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@karl.sch1983 wrote:

...Maybe I need to call geCir1.center() everytime? 

---

Yes of course, as far as you using reference to method and not to variable.

[tbrammer · Accepted solution]

	AcGeCircArc2d geCir1(AcGePoint2d(1, 1), 5);
	AcGePoint2d& geCtr1 = geCir1.center();  //NO!!
	AcGePoint2d geCtr2 = geCir1.center();  //ok.

If you would use the /permissive compiler option your code wouldn't even compile! You would get this error:

error C2440: "Initialisierung": Can't convert "AcGePoint2d" to "AcGePoint2d &"

It is misleading and may cause crashes to initialize a reference with an object that was retured from a function.

The reference AcGePoint2d &geCtr1 does NOT point to the centerpoint of geCir1, but to a temporary copy of it. When this temporary object goes out of scope, the reference becomes invalid.

[karl.sch1983]

Thanks @Alexander.Rivilis  and @tbrammer it makes sense now. I didn't realize I was assigning a reference to a function. In my head I was thinking of it as a property of some primitive type which it clearly is not.

Thanks @zrobert  for the link. It helps too.