#### Archived

This topic is now archived and is closed to further replies.

This topic is 6485 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

I would like to overload the ++ operator. I did it for pre-fix (i.e. ++myclass) but I don''t understand how to overload the postfix++ it (i.e. myclass++). Thanks for your help, Mike

##### Share on other sites
The ++ pre-fix and post-fix operators are the same, the only difference is that with the postfix first the current command is exexcuted and then the ++ operator, with the prefix it''s the other way round. There shouldn''t be a difference with overloaded operators.

GA

##### Share on other sites
Sorry ga, there is a difference...

The prefix version:

aclassfunction operator++ ()
{
}

The post-fix version:

aclassfunction operator++(int)
{
}

The ''int'' is just a dummy argument, thats it. Very subtle but very important!

Cheers

Matt

Check out my project at: www.btinternet.com/~Matthew.Bennett

##### Share on other sites
DataType operator++ ( DataType& a )
{
// prefix
a.item++;
return a;

// postfix
DataType temp = a;
a.item++;
return temp;
}

##### Share on other sites
3dModelMan is correct: the postfix operator++ needs a dummy argument of int. The prefix operator++ doesn''t need it.

Make sure that you''re returing the correct value: the postfix operator++ should return the value before the increment, the prefix operator++ should return the value after the increment. Of course you''re allowed to use different semantics, but it''ll confuse the users of your code.

Erik

##### Share on other sites
Yeah, I knew it needed something. Thanks for your help.

Mike

##### Share on other sites
Anonymous,

++ is a unary operator, that function won''t work.

##### Share on other sites
quote:
Original post by Kaellaar

Anonymous,

++ is a unary operator, that function won''t work.

Is it not possible to declare it that way if you made it a friend function of the class rather than a member?

##### Share on other sites
I''m sorry for my wrong answer. I never needed overloading the ++ operator so I really didn''t expect that there would be a difference to the usual ++ operator.

GA

##### Share on other sites
I don''t think so, I may be wrong, but I dont'' even think the compiler will let you put anything but an int as a parameter.

##### Share on other sites
If you don''t overload both, the compiler just uses the overloaded one for both cases.

class USDollar{public:USDollar() : nDollars(0), dCents(0) {};protected:unsigned int nDollars;double dCents;public:USDollar& operator++();};USDollar& USDollar::operator++(){dCents++;if( dCents >= 100 ){dCents = 0;nDollars++;}return( *this );}main(){USDollar MyWallet();// both of these work fine (in simple expressions)MyWallet++;++MyWallet;return 0; // is this necessary? been a while since console apps...}

- null_pointer
Sabre Multimedia

##### Share on other sites
people who said you need a dummy argument are correct.

e.g.

class poo
{
int x;
poo operator++();
poo operator++(int notused);
};

// then just define the member functions

I looked that up in TYC++ third edition
just before making up that crappy example
the compiler distinguishes between the
pre and post-fix operators by that argument,
and in any calling case, it is passed the value of
zero.

Take it easy,

-Mezz