c++从汇编角度观看指针访问内存地址_mov rcx,qword ptr-优快云博客

文章讨论了在C++中，通过直接对象和指针来访问结构体成员变量的不同方式。直接对象访问是直接对内存地址进行赋值，而指针访问则涉及取指针地址、计算成员变量偏移量的过程。两种方法在汇编层面上有明显的区别，指针访问通常需要额外的步骤来定位成员。

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1直接对象访问成员

#include<iostream>
using namespace std;
int main() {
	struct Person
	{
		int m_id;
		int m_age;
		int m_height;
		void display() {
			cout << "m_id=" << m_id << endl;
			cout << "m_age=" << m_age << endl;
			cout << "m_height=" << m_height << endl;
		};
	};
	Person person;
	person.m_id = 10;
	person.m_age = 20;
	person.m_height = 30;
	person.display();
	//Person* p = &person;
	//p->m_id = 10;
	//p->m_age = 20;
	//p->m_height = 30;
	//p->display();


	//Person* p1 = (Person*)&person.m_age;
	////p1->m_id = 10;
	//p1->m_id = 40;
	//p1->m_age = 50;
	//p1->display();
	////person.display();
	return 0;
}

对应汇编

解释：

显然直接每次赋值直接一步到位，0Ah即10，赋值给[ebp-14h]这个地址，[eb0-14h]==m_id的地址==Person的地址

后面的_age和_height即在0Ah+4=14h 0Ah+4+4=1Eh

[ebp-10h]==_age地址

[ebp-0Ch]==_heigh地址.

2通过指针访问成员

#include<iostream>
using namespace std;
int main() {
	struct Person
	{
		int m_id;
		int m_age;
		int m_height;
		void display() {
			cout << "m_id=" << m_id << endl;
			cout << "m_age=" << m_age << endl;
			cout << "m_height=" << m_height << endl;
		};
	};
	Person person;



	//person.m_id = 10;
	//person.m_age = 20;
	//person.m_height = 30;
	//person.display();
	Person* p = &person;
	p->m_id = 10;
	p->m_age = 20;
	p->m_height = 30;
	p->display();


	//Person* p1 = (Person*)&person.m_age;
	////p1->m_id = 10;
	//p1->m_id = 40;
	//p1->m_age = 50;
	//p1->display();
	////person.display();
	return 0;
}

对应汇编

lea rax,[rbp+8]
mov qword ptr [rbp+38h],rax
mov rax,qword ptr [rbp+38h]
mov dword ptr [rax],0Ah
mov rax,qword ptr [rbp+38h]
mov dword ptr [rax+4],14h
mov rax,qword ptr [rbp+38h]
mov dword ptr [rax+8],1Eh
mov rcx,qword ptr [rbp+38h]