On Friday 03 June 2005 15:09, Filipe Sousa wrote:
> On Friday 03 June 2005 13:46, Mws wrote:
> > hi,
> >
> > in my understanding a singleton is used to have a class
> > instanciated only for one time.
> >
> > normally this is done by
> >
> > having the "wanted-to-be-singleton-class" derived/inherited from
> > a singleton class or template.
> > never ever from the outside ctors are called, but there should be
> > a getInstance() method that checks for _m_instance == NULL
> > if it is matching creating a new instance with new, otherwise returning the
> > _m_instance pointer.
>
> A templated version
>
> template<class T>
> class singleton {
> public:
> static T* instance() {
> if (!m_instance)
> m_instance = new T;
> return m_instance;
> }
>
> private:
> static __attribute__ ((visibility("default"))) T* m_instance;
> };
>
> class __attribute__ ((visibility("default"))) my_singleton : public
> singleton<my_singleton> {
> public:
> my_singleton() { std::cout << __PRETTY_FUNCTION__ << std::endl; }
> };
>
> > if you want to, i can provide you with a complete singleton template.
>
> Yes, please
>
> > regards
> > mws
>
>
singleton.h
#ifndef __singleton__
#define __singleton__
template<class IMPLEMENTINGCLASS>
class TSingleton
{
private:
static IMPLEMENTINGCLASS* instance;
public:
static IMPLEMENTINGCLASS* getInstance()
{
//debugging purposes
std::cout << "before" << instance << std::endl;
if(!instance)
{
instance = new IMPLEMENTINGCLASS();
}
std::cout << "after" << instance << std::endl;
return instance;
}
void dispose()
{
if(instance)
{
delete instance;
instance = NULL;
}
}
};
template<class IMPLEMENTINGCLASS> IMPLEMENTINGCLASS* TSingleton<IMPLEMENTINGCLASS>::instance = NULL;
#endif
usage is like
class CFoo:public TSingleton<foo>
{
private:
CFoo();
virtual ~CFoo();
public:
...
...
};
in case of debugging this you should do a std::cout << instance << std::endl;
instead of mentioning that the ctor is called.
int main() {
// get the instance
CFoo::getInstance();
CFoo::getInstance();
// free mem - call dtor
CFoo::dispose();
return 0;
}
that's what i would do
regards
mws
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