用模板技术判断一个类型是否为类解决思路

// traits/isclasst.hpp

template <typename T>
class IsClassT
{
private:
    typedef char One;
    typedef struct { char a[2]; } Two;
    template<typename C> static One test(int C::*);
    template<typename C> static Two test(...);
public:
    enum { Yes = sizeof(IsClassT<T>::test<T>(0)) == 1 };
    enum { No = !Yes };
};

//traits/isclasst.cpp

#include "isclasst.hpp"
#include <iostream>

using namespace std;

class MyClass
{
};

struct MyStruct
{
};

union MyUnion
{
};

void myfunc()
{
}

enum E { e1 } e;

// Check by passing type as template argument
template <typename T>
void check()
{
    if (IsClassT<T>::Yes)
    {
        cout << " IsClassT " << endl;
    }
    else
    {
        cout << " !IsClassT " << endl;
    }
}

// Check by passing type as function call argument
template <typename T>
void checkT(T)
{
    check<T>();
}

int main()
{
    cout << "int:       ";
    check<int>();

    cout << "MyClass:   ";
    check<MyClass>();

    cout << "MyStruct:  ";
    MyStruct s;
    checkT(s);

    cout << "MyUnion:   ";
    check<MyUnion>();

    cout << "enum:      ";
    checkT(e);

    cout << "myfunc():  ";
    checkT(myfunc);
}