學生時代筆記，可能有誤？

不考慮virtual function

c++ sample class
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class Base {
    public:
        void foo();
    private:
        int i;
        static int si;
}
Base base = Base()
object memory layout
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base:
  int i
Out Of base(like global):
  static int si
  void foo(this) //this pointer point to reference object

考慮繼承與virtual function

c++ sample class
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class Base {
    public:
        virtual void foo();
    private:
        int i;
}
class Derived : Base {
    public:
        virtual void foo();
    private:
        int j;
}
Base *base = new Derived();
base.foo(); //會呼叫Derived的foo
object memory layout
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base:
  Vtable* vtable
  int i
derived:
  Base portion:
    Vtable* vtable
    int i
  int j
vtable:
  function pointer
  function pointer
  ...

Compiler在編譯期間會對Base與Derived的vtable塞入其foo的function pointer
Base vtable 塞 Base的foo的function pointer(compiled time)
Derived vtable 塞 Derived的foo的function pointer(compiled time)
當runtime時確定base的type後base.foo會根據derived裡的vtable去找到foo的真正位置

Reference

The virtual table