how to make const lvalue a constant

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C++

const box& operator++()  //postfix
	{
		const box& b = *this;

		this->width++;
		this->height++;
		this->length++;

		return b;
	}

here is my code. but this displays incremented values even if lvalue is a constant.

this can be done without problem like this..

C++

box operator++()  //postfix
	{
		const box b = *this;

		this->width++;
		this->height++;
		this->length++;

		return b;
	}

But the thing is I want to do this with lvalue references. I mean I want to return a "box&" thing without incrementing it's values.

How can I do it ?

Thanks in advance.

Posted 30-May-14 3:26am

Mark

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[no name] 30-May-14 9:51am

These are prefix overloads. Postfix usually implemented using prefix.

Mark 30-May-14 10:20am

Well. I want to make ++ a postfix with operator overloading

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Stefan_Lang · Answer 1 · 2014-06-01T21:22:00

The second version is correct and shouldn't be changed! The return value must be the value of the instance before incrementation. That value can only be a copy - if it were an lvalue and being modified, the result of the combined modification (with the increment) would be undefined.

If you want to modify as well as increment the object, either do the modification before calling the increment operator (in a separate statement), or use prefix increment. That way the order of modifications is unambiguous.