Operator overloading on "default" operator

[John Smith]

Hello,

I made a class which works like bool primitive but has some special
properties.
Now I want to be able to overload an operator to be able to do the
following:

while (myObj)
{
....
}

It must return true/false naturally, but I'm unsure if it's actually
possible and if so which operator I should overload.

Thanks in advance.
-- John

[Karl Heinz Buchegger]

Re: Operator overloading on "default&q uot; operator

John Smith wrote:[color=blue]
>
> Hello,
>
> I made a class which works like bool primitive but has some special
> properties.
> Now I want to be able to overload an operator to be able to do the
> following:
>
> while (myObj)
> {
> ...
> }
>
> It must return true/false naturally, but I'm unsure if it's actually
> possible and if so which operator I should overload.
>
> Thanks in advance.
> -- John[/color]

class A
{

operator bool() { /* do whatever you need to do and return
a boolean value */ }
};

--
Karl Heinz Buchegger
kbuchegg@gascad .at

[Ivan Vecerina]

Re: Operator overloading on "default&q uot; operator

"Karl Heinz Buchegger" <kbuchegg@gasca d.at> wrote in message
news:4163C07D.4 D618094@gascad. at...[color=blue]
> John Smith wrote:[color=green]
>>
>> Hello,
>>
>> I made a class which works like bool primitive but has some special
>> properties.
>> Now I want to be able to overload an operator to be able to do the
>> following:
>>
>> while (myObj)
>> {
>> ...
>> }
>>
>> It must return true/false naturally, but I'm unsure if it's actually
>> possible and if so which operator I should overload.[/color][/color]
....[color=blue]
> class A
> {[/color]
public: // added for the sake of the discussion below[color=blue]
> operator bool() { /* do whatever you need to do and return
> };[/color]

This is the "obvious" solution, but has well-known caveats,
because bool-s are implicitly convertible to int.
For example, the following expressions become valid:
A a;
int b = 5+a;
a << 5;

This is why usually library writers now prefer to provide
a conversion operator to void* or to a (member) function pointer.
For a discussion, see for example:

http://www.artima.com/cppsource/safebool.html

My personal preference, for internal code, is to implement
operator ! only, because I like to use !! to explicitly
convert values to bool -- e.g. I prefer if( !! myPtr )
to if( myPtr != NULL ) or if( myPtr ) .


Cheers,
Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form