how to access the callback meg c++ code example

Example: c++ callback function

// C++ callback function

class Base {
public:
  void doSomething() {
    using namespace std::placeholders;
    // std::placeholders::_1 is for the callback parameter
    // use _1 for 1 argument
    // or _1, _2, _3 for 3 arguments and so on
    something.setCallback(std::bind(&Base::callback, this, _1));
    // std::bind is needed, otherwise 
    // the callback function would need to be static
  }
  
  // Callback function
  void callback(int i) {
    std::cout << "Callback: " << i << std::endl;
  }
}