Re: understanding singleton design pattern

Rolf Magnus <>
Sun, 18 Jan 2009 20:03:05 +0100
Marcel M??ller wrote:

Instead of the singleton design pattern, if the above function is
used, what are the drawbacks of using the above function ? What are
the advantages of singleton design pattern over the above function ?

The constructor of Test must be public for the above to work. So the
compiler would not reject, when a second instance of Test is created. It
is only up to the programmer whether to use Test as a singleton or not.
Of course alternatively you could make getTestInstance a friend of Test.
But making it a static member of Test is more clear.

Furthermore if the application should provide a defined behaviour at
shutdown, you must delete Test somewhere.
   static boost::scoped_ptr<Test> instance;
will do this job for you. If you do not have boost, std::auto_ptr is
fine too.

In that case, there is no point (no pun intended) in using a pointer. You
can simply create an instance directly. However, both have another issue.
See entries about "static initialization order fiasco" in the FAQ.

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