operator+= or operator+ first?

[tecknophreak]

i can't remember which should be written first. for some reason i seem to remember operator coming first.

[debiandude]

In C its +=, which makes sense becuase =, +=, and -= are evaluted from right to left. i =-b would set i equal to the negative of b, since the minus is on the right modifies b before setting i equal to it.

[ 17 April 2002: Message edited by: debiandude ]

[kmj]

Originally posted by tecknophreak:
<STRONG>i can't remember which should be written first. for some reason i seem to remember operator coming first.</STRONG>

What do you mean by the phrase "written first"? If you mean time-wise then probably the operator+, so that you can use it when you write operator+=; of course, you probably also want to have operator= written too. Of course, I'm just guessing at what you're asking, and I'm assuming that debiandude guessed wrong at what you were asking. So, please be a little more clear in what your asking... (c:

[bwkaz]

Err?

I think he means "which one should I write first, and which one should use the other?"

Like if he wrote operator += first, then operator + would create a temporary object (initialized to whatever got passed in), then he'd use += on it to add the other argument, then he'd return a copy of the temporary.

If he wrote operator + first, then he could use it in operator +=, with the same end result.

And as a matter of fact, I have no idea which is "supposed" to be done first either.

[tecknophreak]

bwkaz was right. when i was taking some c++ courses, i was told that if you wrote one first(like +=) then use it when writing +, it'll be faster than if you write + first and use it in writing +=. however i have forgotten.

Sorry bout the confusion.

[debiandude]

Woah I guess I was totllly off base with that one. I should have know becuase I seen some code that you have posted before techno so I don't know I didn't just realize that you obviously wouldn't ask such a rudimentary question. So this was about some wierd C++ mumbo jumbo ;-) I prolly should look in to C++ maybe someday.

[tecknophreak]

my bad. i'll have to start adding some more info on my posts. :( C++ mumbojumbo.. c++ is good. me like

[tecknophreak]

just for an update, you should create operator+= first then use it when creating operator+.

when you use operator+, you need to create a new container. when you use operator+= you don't. so if you use operator+ in operator+=, you're creating a new container which you don't need to create.

hope this makes some sense.

[Stuka]

OK, the not making a container makes sense, but I'm having difficulty with using += in +....

[tecknophreak]

i'll have to get back to you on that one...i forgot how to make it so. :rolleyes:

[bwkaz]

Just for example, assume MyClass is a wrapper for ints or something. The only private member is "value":

void operator +=(MyClass &a, const MyClass &b)
{
a.value += b.value;
}

MyClass operator +(const MyClass &a, const MyClass &b)
{
MyClass c = a; // Assumes that MyClass::operator =(const MyClass &) has been properly defined and implemented

c += b;

return c;
}

Make sense?

[ 25 April 2002: Message edited by: bwkaz ]

[Stuka]

Ahh...makes perfect sense...