Re: what's wrong with the following singleton class???

"Alf P. Steinbach" <>
Sun, 30 Apr 2006 07:26:21 +0200
* Alf P. Steinbach:


// T.h:

class T
    static T* instance();
    T() {}
    ~T() {}
    static T* smInstance;

// T.cpp:

T* T::instance()
  if (smInstance == NULL)
    smInstance = new T();

  return smInstance;

when I try to compile the above code, there is linker error:
../T.cpp:3: undefined reference to `T::smInstance`

I am using gcc 3.4.6 under gentoo linux, thanks

You have declared but not defined 'smInstance'.

It should be defined in your [T.cpp] file.

But instead, just do

  class T
      T() {}
      T( T const& );
      ~T() {}
      static T& instance()
          T theInstance;

Should be

             static T theInstance;

of course.

          return theInstance;

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