Question

A constructor assembles the execution environment for the member
functions for a class from the bottom up (members first). The
destructor disassembles it from the top down (members last).

[from C++ programming language]

please can someone describe this? I understand that members functions means here members functions of the class, but what "members" first? is this related to function on the stack? what means "assembles the execution environment"?

Answer 1

The sentence is quite abstract. The execution environment of a a member function are the members of the class itself and members exposed by one of the base-classes.

Presumably, what is meant by “assemble the execution environment”, is to initialize all members and bases of the class (note that member functions don’t need to be initialized).

I don’t see how this would relate to an object being on the stack or not.

An example:

class X {
public:
  X() // constructor initializes first a, then b, then c
  {
    // members are now accessible for member functions
    foo();
  }

  void foo() {
    // member function executes in the context of an object
    // a, b, and c mean this->a, this->b and this->
    std::cout << a << b << c << std::endl;
  }

  ~X() {} // destroys first c, then b and then a 
private:
  int a;
  double b;
  char c;
};

Please note that you don’t need to write out the destructor in the
above case. This is just done for exemplary purposes here.