C++: Undefined reference to instance in Singleton class

Question

I\'m currently trying to implement a factory as a singleton. I practically used the textbook example of the Singleton pattern. Here\'s the .h file:

namespace         


        

Answer 1

You must define the static instance, not just declare it. The definition creates the actual object you refer to.

In your cpp file, add the line:

boost::shared_ptr ImpFactory::mInstance;