《Itanium C++ ABI》文档2.3节中描述:
A pointer to data member is an offset from the base address of the class object containing it, represented as a ptrdiff_t. It has the size and alignment attributes of a ptrdiff_t. A NULL pointer is represented as -1.
测试一:
// test.cpp
#include <iostream>
#define PRINT(var) do { std::cout << (var) << std::endl; } while(0)
class CTest
{
public:
int a;
int b;
};
int main()
{
int CTest::*p0 = 0;
int CTest::*p1 = &CTest::a;
int CTest::*p2 = &CTest::b;
PRINT(*(long *)(&p0));
PRINT(*(long *)(&p1));
PRINT(*(long *)(&p2));
return 0;
}
输出结果为:
-1
0
4
测试二:
// test.cpp
#include <iostream>
#define PRINT(var) do { std::cout << (var) << std::endl; } while(0)
class Base
{
public:
int a;
int b;
};
class Derived : public Base
{
public:
int c;
int d;
};
int main()
{
int Derived::*p1 = &Derived::a;
int Derived::*p2 = &Derived::b;
int Derived::*p3 = &Derived::c;
int Derived::*p4 = &Derived::d;
PRINT(*(long *)(&p1));
PRINT(*(long *)(&p2));
PRINT(*(long *)(&p3));
PRINT(*(long *)(&p4));
return 0;
}
输出结果为:
0
4
8
12
原文链接: https://www.cnblogs.com/opangle/archive/2012/08/27/2658418.html
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