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C++ destructors

Started by Pipo DeClown Jan 5, 2003 at 9:53 AM 9 replies 250+ views

Original Post

Jan 5, 2003 at 9:53 AM

Does C++ destroy instances in the opposite order? Construction: class cClass { public: cClass2 Class2; sStruct* LinkedList; int numberofstructsinlist; cClass(); ~cClass(); }; So the Destruction: Every sStruct beginnin at the tail, ending at the head. Then the cClass2 Then the cClass. Am I correct? Report to moderator .lick

civguy

Jan 5, 2003 at 11:53 AM

Not quite so.

First cClass destructor, then cClass2 destructor. And your sStruct* won''t be destroyed at all unless you destroy it in cClass destructor.

But the order is opposite to construction. cClass2 is constructed first, then cClass.

Pipo DeClown

Jan 5, 2003 at 12:00 PM

I mean if sStruct has a destructor...

.lick

Ziphnor

Jan 5, 2003 at 12:07 PM

sStruct still wont be destroyed, its only a pointer, and pointers doesnt have destructors(even if the object they point to have).
If you want to call its destructor youll have to "delete LinkedList;" it in ~cClass().

civguy

Jan 5, 2003 at 12:08 PM

It doesn''t matter whether it has a destructor or not, if it isn''t called anywhere. It can be called explicitely, or usually through "delete LinkedList;"

Pipo DeClown

Jan 5, 2003 at 12:15 PM

hmm...

say if the I allocated memory for them though runtime...
the destructors should be called right?

~sStruct()
{
// safety checks
delete Next;
}

~cClass()
{
// safety checks
delete LinkedList;
}

~cClass2()
{
}

......

destruct order would be:
~tail();
~between();
~head();
~class2();
~class();

TRUE?!!!!!

.lick

civguy

Jan 5, 2003 at 12:23 PM

You can try it out easily. Just put some "cout"s in the destructors.

SabreMan

Jan 5, 2003 at 1:30 PM

quote:
Original post by Pipo DeClown
Does C++ destroy instances in the opposite order?

For objects which go on the stack, yes. That''s a property of a stack: last-in first-out.

quote:

Every sStruct beginnin at the tail, ending at the head.

No. Heap-based objects get destructed when you explicitly delete them, in the order that you delete them.

Stoffel

Jan 5, 2003 at 1:49 PM

quote:
Original post by Pipo DeClown
~sStruct()
{
// safety checks
delete Next;
}

Sounds like you''re having each sStruct delete the next in the list. This is a Bad Thing. It''s inefficient & stack-hungry. You should instead have the LinkedList destructor delete each sStruct itself.

Pipo DeClown

Jan 5, 2003 at 2:06 PM

Okay, thanks.
Btw, this "Bad" thing is a thing that moderator Jim does

.lick

Stoffel

Jan 5, 2003 at 5:26 PM

That doesn''t make it any less of a Bad Thing.

T h i n k L i b e r a l l y .

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