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Vetinari

++ operator overloading

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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

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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.

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GA

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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

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Guest Anonymous Poster
DataType operator++ ( DataType& a )
{
// prefix
a.item++;
return a;

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

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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

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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?

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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

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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

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