c++ offset define

#include <iostream>

using namespace std;

class test {

public:

void show() {

cout << y << '\n';

}

public:

int x = 10;

int y = 20;

};

#define offset_(x, yy) ((size_t)&((x *)nullptr)->y)

int main() {

test a;

int y = *(int *)((uint64_t)&a + offset_(test, y));

cout << y << '\n';

a.show();

return 0;

}

offset的宏实现

OFFSET_OF(TYPE, FIELD) ((size_t)&((TYPE*)nullptr)->FIELD)

虚继承时offset会出现负的情况