How to ensure that a method is executed only once for the lifetime of that object?

Question

class MyObj{ public:     void myFunc(){          //ToBeExecutedJustOnce     }  }; 

I have a function that I want to be executable only once for the lifetime of MyObj. There may be many instances of MyObj, and each should be able to execute that function once. So if I have:

MyObj first; MyObj second; MyObj third: first.myFunc(); // Should execute second.myFunc(); // Should execute third.myFunc(); // Should execute first.myFunc(); // Should not execute second.myFunc(); // Should not execute third.myFunc(); // Should not execute 

Options:

1. member variable: If I use a member variable, then other functions within MyObj can access it and change it.
2. global static variable: Can't work because first,second and third will all be checking the same variable.
3. local static: Same problem as #2.

The only solution I have found, is to have MyObj inherit from another class

MyOtherObj{ private:     bool _isInit = false; public:     bool isInit(){           bool ret = true;           if (!_isInit){               ret = false;               _isInit = true;           }           return ret;     } };  class MyObj : public MyOtherObj { public:     void MyFunc(){         if (!isInit()){             //Do stuff...         }     }   }; 

Any better suggestion ?

EDIT: I don't care about thread safety!

EDIT: I do not want to execute the method in the constructor, simply because the method may need to be executed much later in the lifetime of the object....

Answer 1

Use std::once_flag. It is not resettable from other methods (then again, if you cannot trust other methods of the same class, your development process is highly questionable), easy to use, and it is even thread-safe if you ever do care about that. It can be a bit less efficient in a single-threaded program.

#include <mutex>  class MyObj { public:     void MyFunc() {         std::call_once(initFlag, [=] {                 //Do stuff...             });     }  private:     std::once_flag initFlag; };