Re: destructor is not getting called for singleton

From:
Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Fri, 29 Apr 2011 17:35:54 CST
Message-ID:
<4p2q88-ra.ln1@satorlaser.homedns.org>
Note up front: You would have had an easier time figuring things out if you
had removed the template<...> first. Also, Singleton.hpp is missing and you
should have put the whole thing into a single translation unit and test
compiled it!

Anyhow...

Harry wrote:

template <class T>
T * Singleton<T>::_instance = 0;


The class Singleton holds a single T and helps creating one. It references
the singleton via a class-static pointer, right?

template <class T>
Singleton<T>::~Singleton()
{
std::cout<<"Singlton Destructor Called"<<std::endl;
     delete _instance;
}

[...]

int main()
{
   single::instance().test();
   return 0;
}


Here, you are referencing the class Singleton<A> here, but you are not
instantiating it anywhere. Consequently, the destructor is never called as
there are no instances to destroy here.

BTW: Consider what would happen if you created two instances of this
Singleton<A>. Both would refer to the same underlying A instance, but the
first Singleton to be destroyed would also destroy that A instance. This is
probably not what you want.

Suggestion: Don't use a raw pointer but use a std::auto_ptr instead.

Uli

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