Re: [Dev-C++] singleton pattern implementation.

Hello,

The question to ask: is there a need to release the memory reserved for
the singleton? In other words:
* Does the singleton lives from the moment where is is created (the
first call to newInstance()) till the end of your application (no need
to release it)?
* Or should it disappear before the end of the application (the related
memory should be released)?

If the answer is No, and this is my feeling, just forget about it. When
your application will end, the system will get back its memory
automatically.

If for any reason the answer is Yes, then add a member method to your
class ('deleteInstance' for example) that will:
* delete the singleton 'delete singleton;'
* set the singleton to NULL: 'singleton = NULL;' (by the way, your can
forget about 'instanceFlag' and test only on 'singleton' value: NULL
means allocate, Not NULL, don't allocate)

And call this method at the moment where you like to release the memory
linked to the singleton.

Nota Bena: don't mix allocate/free with new/delete. They are completely
different and doesn't like each other.

Have a nice evening.

Younes


On Thu, 2007-09-27 at 08:09 -0700, Chris Miller wrote:
> On 9/27/07, Laura Lozano <lau...@gm...> wrote:
> > Hello,
> >
> > I have a question about the next implementation of the singleton patter, if
> > I don't do "delete sc1" in main, is there a memory leak?  the problem is
> > that if I do in the destructor "delete single"  it produces an infinite
> > loop.
> 
> I'm not speaking from experience, but just thinking aloud.
> 
> You don't need to call delete in the destructor.  Remember, a class is
> literally just a bunch of locations in memory.  If the destructor has
> been called, delete has already been called (externally to the
> destructor) as well.  IIRC, it's your job to free all pointers to
> locations in memory that are handled by the class in the destructor,
> since those won't be freed automatically by delete.
> 
> > How could I free the memory associated to the variable single?
> 
> Perhaps use free(single)?  I'm not sure, I know there are consequences
> to mixing new/delete and malloc/free, but from my (rather limited)
> knowledge I know that free() will just release memory back to the
> system.
> 
> > Thank you.
> >
> > class Singleton
> > {
> >
> private:
> >  static bool instanceFlag;
> >  static Singleton *single;
> >  Singleton()
> >  {
> >
> //private constructor
> >  }
> > public:
> >  static Singleton* getInstance();
> >  void method();
> >  ~Singleton()
> >  {
> >  instanceFlag = false;
> >  }
> > };
> >
> > bool Singleton::instanceFlag = false;
> > Singleton* Singleton::single = NULL;
> > Singleton* Singleton::getInstance()
> > {
> >  if(! instanceFlag)
> >  {
> >  single = new Singleton();
> >  instanceFlag =
> true;
> >  return single;
> >  }
> >  else
> >  {
> >  return single;
> >  }
> > }
> >
> >
> void Singleton::method()
> > {
> >  cout << "Method of the singleton class" << endl;
> > }
> >
> > int main()
> > {
> >  Singleton *sc1;
> >  sc1 = Singleton::getInstance();
> >  sc1->method();
> >
> >  return 0;
> > }
> >
> >
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> 
> 
-- 
Younes