C++继承时的对象内存位置(一)
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C++继承时的对象内存位置(一)
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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);
}
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();obj_b.display();return 0;
}
&obj_a.m_a=0x7ffc9098d234 &obj_a.m_b=0x7ffc9098d238 &obj_a=0x7ffc9098d234
&obj_b.m_a=0x7ffc9098d23c &obj_b.m_b=0x7ffc9098d240 &obj_b.m_c=0x7ffc9098d244 &obj_b=0x7ffc9098d23c
m_a=99, m_b=10
m_a=84, m_b=23, m_c=95
obj_a 是基類對象，obj_b 是派生類對象。假設 obj_a 的起始地址為 0X1000，那么它的內存分布如下圖所示：
假設 obj_b 的起始地址為 0X1100，那么它的內存分布如下圖所示：
可以發現，基類的成員變量排在前面，派生類的排在后面。
為了讓大家理解更加透徹，我們不妨再由 B 類派生出一個 C 類：
#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_d; }; C::C(char a, int b, int c, int d): B(a, b, c), m_d(d){ } void C::display(){printf("m_a=%d, m_b=%d, m_c=%d, m_d=%d\n", m_a, 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();C obj_c(84, 23, 95, 60);cout<<"&obj_c.m_a="<<&obj_c.m_a<<" &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; }假設 obj_c 的起始地址為 0X1200，那么它的內存分布如下圖所示：
成員變量按照派生的層級依次排列，新增成員變量始終在最后。
總結
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