c++ - C++ 中的纯虚函数在哪里？

Question

哪个虚表将是纯虚函数？在基类还是派生类？

比如每个类(class)的虚拟表是什么样子的？

class Base {

  virtual void f() =0;
  virtual void g();
}


class Derived: public Base{

  virtual void f();
  virtual void g();

}

Answer 1

g++ -fdump-class-hierarchy layout.cpp 生成文件 layout.cpp.class。 layout.cpp.class 的内容将显示如下:

Vtable for Base
Base::_ZTV4Base: 4u entries
0     (int (*)(...))0
8     (int (*)(...))(& _ZTI4Base)
16    __cxa_pure_virtual
24    Base::g

Class Base
   size=8 align=8
   base size=8 base align=8
Base (0x7ff893479af0) 0 nearly-empty
    vptr=((& Base::_ZTV4Base) + 16u)

Vtable for Derived
Derived::_ZTV7Derived: 4u entries
0     (int (*)(...))0
8     (int (*)(...))(& _ZTI7Derived)
16    Derived::f
24    Derived::g

Class Derived
   size=8 align=8
   base size=8 base align=8
Derived (0x7ff893479d90) 0 nearly-empty
    vptr=((& Derived::_ZTV7Derived) + 16u)
  Base (0x7ff893479e00) 0 nearly-empty
      primary-for Derived (0x7ff893479d90)

删除 f 的“纯粹性”将第五行更改为:

16    Base::f