C++继承时的对象内存位置(一)有成员变量遮蔽时的内存分布
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C++继承时的对象内存位置(一)有成员变量遮蔽时的内存分布
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#include <cstdio>
#include<iostream>
using namespace std;
//基類A
class A{
public:A(int a, int b);
public:void display();public:int m_a;int m_b;
};
A::A(int a, int b): m_a(a), m_b(b){}
void A::display(){printf("m_a=%d, m_b=%d\n", m_a, m_b);
}
//派生類B
class B: public A{
public:B(int a, int b, int c);void display();public:int m_c;
};
B::B(int a, int b, int c): A(a, b), m_c(c){ }
void B::display(){printf("m_a=%d, m_b=%d, m_c=%d\n", m_a, m_b, m_c);
}//聲明并定義派生類C
class C: public B{
public:C(char a, int b, int c, int d);
public:void display();
public:int m_b; //遮蔽A類的成員變量int m_c; //遮蔽B類的成員變量int m_d; //新增成員變量
};
C::C(char a, int b, int c, int d): B(a, b, c), m_b(b), m_c(c), m_d(d){ }
void C::display(){printf("A::m_a=%d, A::m_b=%d, B::m_c=%d\n", m_a, A::m_b, B::m_c);printf("C::m_b=%d, C::m_c=%d, C::m_d=%d\n", m_b, m_c, m_d);
}int main(){A obj_a(99, 10);B obj_b(84, 23, 95);cout<<"&obj_a.m_a="<<&obj_a.m_a<<" &obj_a.m_b="<<&obj_a.m_b<<" &obj_a="<<&obj_a<<endl;cout<<"&obj_b.m_a="<<&obj_b.m_a<<" &obj_b.m_b="<<&obj_b.m_b<<" &obj_b.m_c="<<&obj_b.m_c<<" &obj_b="<<&obj_b<<endl;obj_a.display();
//創建C類對象obj_cC obj_c(84, 23, 95, 60);obj_c.display();cout<<"&obj_c.m_a="<<&obj_c.m_a<< " &obj_c.A::m_b="<<&obj_c.A::m_b<< " &obj_c.B::m_c="<<&obj_c.B::m_c<<" &obj_c.m_b="<<&obj_c.m_b<<" &obj_c.m_c="<<&obj_c.m_c<<" &obj_c.m_d="<<&obj_c.m_d<<" &obj_c="<<&obj_c<<endl;obj_c.display();obj_b.display();return 0;
}
&obj_a.m_a=0x7fffc1edf9dc &obj_a.m_b=0x7fffc1edf9e0 &obj_a=0x7fffc1edf9dc
&obj_b.m_a=0x7fffc1edf9e4 &obj_b.m_b=0x7fffc1edf9e8 &obj_b.m_c=0x7fffc1edf9ec &obj_b=0x7fffc1edf9e4
m_a=99, m_b=10
A::m_a=84, A::m_b=23, B::m_c=95
C::m_b=23, C::m_c=95, C::m_d=60
&obj_c.m_a=0x7fffc1edf9f0 &obj_c.A::m_b=0x7fffc1edf9f4 &obj_c.B::m_c=0x7fffc1edf9f8 &obj_c.m_b=0x7fffc1edf9fc &obj_c.m_c=0x7fffc1edfa00 &obj_c.m_d=0x7fffc1edfa04 &obj_c=0x7fffc1edf9f0
A::m_a=84, A::m_b=23, B::m_c=95
C::m_b=23, C::m_c=95, C::m_d=60
m_a=84, m_b=23, m_c=95
假設 obj_c 的起始地址為 0X1300,那么它的內存分布如下圖所示
當基類 A、B 的成員變量被遮蔽時,仍然會留在派生類對象 obj_c 的內存中,C 類新增的成員變量始終排在基類 A、B 的后面。
總結:在派生類的對象模型中,會包含所有基類的成員變量。這種設計方案的優點是訪問效率高,能夠在派生類對象中直接訪問基類變量,無需經過好幾層間接計算。
總結
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