C++类的内存分布

C++一般类的内存分布

一下都是在x64下进行的编译

1、空类

2、无继承、无虚函数类

3、无继承、有虚函数类

4、有继承、有虚函数类

C++继承类的内存分布

C++多重继承时的内存分布

#include <iostream>
using namespace std;

class A {
public:
    int a;
};

class B1 :  public A {
public:
    int b1;
};

class B2 :  public A {
public:
    int b2;
};

class C : public B1, public B2 {
public:
    int c1;
};

int main() {
    
    cout << "A_size=" << sizeof(A) << endl;
    cout << "B1_size=" << sizeof(B1) << endl;
    cout << "B2_size=" << sizeof(B2) << endl;
    cout << "C_size=" << sizeof(C) << endl;
    cout << "end..." << endl;
    system("pause");
    return 0;
}

类A、B1、B2的内存分布

类C的内存分布

C++类虚继承时的内存分布---->虚继承解决二义性的问题

#include <iostream>
using namespace std;

class A {
public:
    int a;
};

class B1 : virtual public A {
public:
    int b1;
};

class B2 : virtual public A {
public:
    int b2;
};

class C : public B1, public B2 {
public:
    int c1;
};

int main() {
    C  c1;
    c1.b1 = 100;
    c1.b2 = 200;
    c1.c1 = 300;

    c1.a = 500; //虚继承使得成员变量a只有一份拷贝，通过虚指针可以确定地址

    cout << "A_size=" << sizeof(A) << endl;
    cout << "B1_size=" << sizeof(B1) << endl;
    cout << "B2_size=" << sizeof(B2) << endl;
    cout << "C_size=" << sizeof(C) << endl;
    cout << "end..." << endl;
    system("pause");
    return 0;
}

类A和B1的内存分布

类B2的内存分布

类C的内存分布