[RESOLVED] Can you call a constructor twice

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foo = CFoo(); //init foo with brand new CFoo, almost by calling ctor second time

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ONLY if CFoo has a well formed assignment operator :eek:

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I can't see for the life of me see the purpose of that! All it's doing is making another function do what the constructor does... and once! What I asked was if you can call a constructor twice.

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It makes a difference.
A constructor is NOT a normal member function. It's specially handled by the compiler, and implicitly does a lot of things under the hood, especially when inheritance is involved, moreover it has specific semantics so that when new() is called, the storage gets a new effective type.

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Two people posted the same code but all it does is chuck a function into a constructor that does the constructor's job... I just don't see the point in it.

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Do you know the difference between initialization and assignment?
You're going to get into troubles if you do that!
For example, if your class contains a std::string member, I can claim that with most compilers, the second initialization won't free the memory of the first string, and it'll do a memory leak!

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It's not that important that I find out the answer to this question, but I was just curious because it is easier than creating another function to initiliase a class's

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If you're lazy to such an extent, I guess you don't write many "secondary functions", but write huge functions... That would be a very bad programming style.

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Originally Posted by exterminator

That code posted by Ovidiu uses the placement new operator. But that can be disastrous and it is probably undefined behaviour by the standards. You should not be doing that and that is what Ovidiu tells when he say "(although you may not)."

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No, behavior is defined, but this is evil, and may certainly create memory leaks!

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Originally Posted by basic.life

4 A program may end the lifetime of any object by reusing the storage
which the object occupies or by explicitly calling the destructor for
an object of a class type with a non-trivial destructor. For an
object of a class type with a non-trivial destructor, the program is
not required to call the destructor explicitly before the storage
which the object occupies is reused or released; however, if there is
no explicit call to the destructor or if a delete-expression
(_expr.delete_) is not used to release the storage, the destructor
shall not be implicitly called and any program that depends on the
side effects produced by the destructor has undefined behavior.

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Originally Posted by Mybowlcut

So you can't call a constructor full stop?

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You can indirectly, through placement operator new, but this is evil and will produce memory leak. Bad idea.
Actually, this is "re-using" the memory of the previous object. The old object dies (and memory is likely to leak) while a new object takes its place.

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Originally Posted by Hobson

There is a rule which says something like: Each logical task shoud be performed in dedicated function. And each function should perform only one logical task.

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Very good.
This basic principle of procedural programming must not be forgotten in OOP, because OOP is an extension of the procedural programming paradigm and must keep the good principles.

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Originally Posted by exterminator

You can write code in constructor body (but that is not initialization, that is assignment)

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I would like to tell, so that it becomes clear to everybody, that even when not using the initializer list, constructors of members (and base classes) are implicitly called before the "body" of the constructor is entered.

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Originally Posted by Philip Nicoletti

1) the constructor can not "be called" twice (technically
not even once). (Constructors do not have names and you
can not take the address of the constructor).

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Exactly! And this is the reason why we cannot do explicit instantiation of constructor templates! Here - http://learningcppisfun.blogspot.com...-explicit.html

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Originally Posted by Philip Nicoletti

2) What Ovidiu did was create a SECOND object (but at the
same location as the first). So TWO objects are created,
but only ONE destructor will be called.

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It's like saying somebody can be born twice and be the same (like in my example) or may be qite different (like in your extension).
Now returning to good programming common sense, each of us would be happy to have an Init() method when the destructor is approaching (like the OP purpose and the solution offered here)... :)

Ovidiu

PS. I have heard that every cat has nine constructors. :D ;)

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Originally Posted by TheCPUWizard

ONLY if CFoo has a well formed assignment operator :eek:

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not really. ONLY if there is dynamic allocation in the assigned class AND if CFoo has a assignment operator. there is std::string used so its safe to let the compiler generate a assignment operator

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Originally Posted by ovidiucucu

PS. I have heard that every cat has nine constructors. :D ;)

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so if he dies from age he can live 9 times his age? or will it create a gaia leak in the planet?

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Originally Posted by Mitsukai

not really. ONLY if there is dynamic allocation in the assigned class AND if CFoo has a assignment operator. there is std::string used so its safe to let the compiler generate a assignment operator

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Mitsukai,

If there is no dynamic allocation, and all member variables have fell formed assignment operators, then the default assignment operator will be a well formed assignment operator. Therefore I stand by my original statement.