speed of casts

[Mike -- Email Ignored]

class Base
{
....
}
class Child : public BASE
{
public:
Thing& getThing();
....
}

Base* pBase = new Child;

Base* qBase = pBase;

Now if I verify that:

dynamic_cast<Child*>(qBase) != 0

and I have a lot of dereferencing to do, I
imagine that the code would be faster in I use,
for example:

Thing thing = reinterpret_cast<Child*>(qBase)->getThing();

instead of the usual dynamic_cast.

Is this correct?

Thanks,
Mike.

 

[joecook]

Now if I verify that:

    dynamic_cast<Child*>(qBase) != 0

and I have a lot of dereferencing to do, I
imagine that the code would be faster in I use,

Thing  thing = reinterpret_cast<Child*>(qBase)->getThing();

instead of the usual dynamic_cast.

Is this correct?

"faster" is relative, but dynamic cast does more checking.
Instead of dynamic_cast, you should replace it with static_cast, not
reinterpret_cast in this case.

Joe C

 

[Alf P. Steinbach]

* Mike -- Email Ignored:

class Base
{
...
}
class Child : public BASE
{
public:
Thing& getThing();
...
}

Base* pBase = new Child;

Base* qBase = pBase;

Now if I verify that:

dynamic_cast<Child*>(qBase) != 0

and I have a lot of dereferencing to do, I
imagine that the code would be faster in I use,
for example:

Thing thing = reinterpret_cast<Child*>(qBase)->getThing();

instead of the usual dynamic_cast.

Perhaps. Measure.

Is this correct?

No, and therein lies the rub.


Cheers & hth.,

- Alf