Calling non-static variable from static function

Question

I am a beginner programmer in C++ and doing a PoC for my company. So I apologize for my basic question.

class TestOne{
  private:
    TestTwo* t2;

  void createInstance(TestTwo* param){
    t2 = param;
  }

  static void staticFunctionToAccessT2(){
    // Now here I want to access "t2" here in the current instance of the class
    // By current instance I mean "this" in non-static context
    // currently there is no function to get object, but can be created
    // ** we cannot call new TestOne(), because that will create a new instance
    // ** of the current class and that I don't want.
  }
}

Any help in this regard will be greatly appreciated.

Thanks

===UPDATE===

This can be taken as a scenario in which I am developing an application in QT Creator, where I have a static function of predefined signature and want to access the UI elements for text change(like TextEdit)

Answer 1

You can't do this, even in Java.

static methods are simply local helper functions for all instances of the class with no access to individual class state (for example t2).

Either remove the static from the method, or make the member variable a static variable, depending on what you are trying to accomplish.

EDIT:

If I understand you correctly your SDK wants a function pointer which it will call to modify your instances' t2. Your mutator method should be public and non-static. So let's just say you redefined staticFunctionToAccessT2 like this:

public: void mutateT2();

If the instance you wanted to call mutateT2 on was defined as:

TestOne foo;

Where your SDK wants a function pointer you could pass this in:

std::bind(&TestOne::mutateT2, foo)

As is pointed out by Mike Seymour below this only works if the SDK method parameter is a std::function not if its parameter is a raw function pointer.