float Point3d::* 类型怎么比较大小？

[Microsues]

#include <iostream>
#include<list>
#include<assert.h>
using namespace std;

class Point3d
{
public:
	float x; 
	static list<Point3d*> *freeList;
public:
	float y;
	static const int chunkSize = 250;
public:
	float z;
};

template<class class_type,class data_type1,class data_type2>
char* access_order_t(data_type1 class_type::*mem1,data_type2 class_type::*mem2)
{
	assert (mem1 != mem2);
	return mem1 < mem2 ? "member 1 occurs first" : "member 2 occurs first";
}

int main()
{
	Point3d Pobj;
	if(&Pobj.x < &Pobj.y)
		cout<< "member 1 occurs first" <<endl;
	else
		cout<< "member 2 occurs first" <<endl;
	
	//if(&Point3d::x < &Point3d::y)   // float Point3d::* 类型不能直接比较大小
	cout<< access_order_t(&Point3d::x,&Point3d::y)<<endl;
}

程序编译出错：Error 1 error C2296: '<' : illegal, left operand has type 'float Point3d::* '

请问怎么比较float Point3d::*类型的大小 ？

[bargio_susie]

你想按照哪个数据成员比较呢？？

 return mem1.x < mem2.x ? "member 1 occurs first" : "member 2 occurs first";

按照数据成员x来比较的

[老邓]

#include <iostream>
#include<list>
#include<assert.h>
using namespace std;

class Point3d
{
public:
    float x;
    static list<Point3d*> *freeList;
public:
    float y;
    static const int chunkSize = 250;
public:
    float z;
};

template <typename T>
void* GetMemberFuncAddr(T t)
{
    union
    {
        T from;
        void* to;
    } ut;

    ut.from = t;
    return ut.to;
}

template<class class_type, class data_type1, class data_type2>
char* access_order_t(data_type1 class_type::*mem1, data_type2 class_type::*mem2)
{
    assert(mem1 != mem2);
    return GetMemberFuncAddr(mem1) < GetMemberFuncAddr(mem2) ? "member 1 occurs first" : "member 2 occurs first";
}

int main()
{
    Point3d Pobj;
    if (&Pobj.x < &Pobj.y)
        cout << "member 1 occurs first" << endl;
    else
        cout << "member 2 occurs first" << endl;

    //if(&Point3d::x < &Point3d::y)   // float Point3d::* 类型不能直接比较大小
    cout << access_order_t(&Point3d::x, &Point3d::y) << endl;
}

[老邓]

用一个union来欺骗编译器。

[taodm]

指向成员的指针，比较大小有什么意义？就像指向函数的指针比较，有啥意义？

[QQIANQQ]

[Quote=引用 2 楼 loaden 的回复:]
C/C++ code
#include <iostream>
#include<list>
#include<assert.h>
using namespace std;

class Point3d
{
public:
float x;
static list<Point3d*> *freeList;
public:
float y;
s……
[/Quote]
++不在一个层次上面的 学习了！

[qiaolixian]

return mem1.x < mem2.x ? "member 1 occurs first" : "member 2 occurs first";

[QQIANQQ]

楼主看下http://blog.csdn.net/QQIANQQ/archive/2011/01/17/6146404.aspx