【C++學習】查看C++對象內存佈局

環境

g++ --version
g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

命令：

g++ --std=c++11  -fdump-class-hierarchy main.cpp

代碼和結果

class NullClassObj {

};

class InfoClass {
private:
    int a;
};

class Base {
public:
    Base() {}
    virtual ~Base() {}
    virtual void VFunc() {}
    virtual void VFunc2() {}
private:
    int a;
};


class Derived : public Base {
public:
    Derived() {}
    ~Derived() override {}
    void VFunc() override {}
private:
    int b;
};


int main() 
{
    Base *ptr = new Derived();
    delete ptr;
    return 0;
}

執行g++ --std=c++11 -fdump-class-hierarchy main.cpp，生成如下結果：

Class NullClassObj
   size=1 align=1
   base size=0 base align=1
NullClassObj (0x0x7f2ca7ad0960) 0 empty

Class InfoClass
   size=4 align=4
   base size=4 base align=4
InfoClass (0x0x7f2ca7ad09c0) 0

Vtable for Base
Base::_ZTV4Base: 6 entries
0     (int (*)(...))0
8     (int (*)(...))(& _ZTI4Base)
16    (int (*)(...))Base::~Base
24    (int (*)(...))Base::~Base
32    (int (*)(...))Base::VFunc
40    (int (*)(...))Base::VFunc2

Class Base
   size=16 align=8
   base size=12 base align=8
Base (0x0x7f2ca7ad0a20) 0
    vptr=((& Base::_ZTV4Base) + 16)

Vtable for Derived
Derived::_ZTV7Derived: 6 entries
0     (int (*)(...))0
8     (int (*)(...))(& _ZTI7Derived)
16    (int (*)(...))Derived::~Derived
24    (int (*)(...))Derived::~Derived
32    (int (*)(...))Derived::VFunc
40    (int (*)(...))Base::VFunc2

Class Derived
   size=16 align=8
   base size=16 base align=8
Derived (0x0x7f2ca797d1a0) 0
    vptr=((& Derived::_ZTV7Derived) + 16)
  Base (0x0x7f2ca7ad0ea0) 0
      primary-for Derived (0x0x7f2ca797d1a0)

結果說明

// TODO