#include<type_traits>

template< class From, class To >
struct is_convertible;

template< class From, class To >
struct is_nothrow_convertible;

is_convertible <A*, B*>::value;

// C++程序演示
// std :: is_convertible示例
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

// 给定的类
class A {
};
class B: public A {
};
class C {
};

// 驱动程序
int main()
{
    cout << boolalpha;

    // 检查类B是否可以转换为A
    bool BtoA = is_convertible<B*, A*> :: value;
    cout << BtoA << endl;

    // 检查类A是否可以转换为B
    bool AtoB = is_convertible<A*, B*> :: value;
    cout << AtoB << endl;

    // 检查类B是否可以转换为C
    bool BtoC = is_convertible<B*, C*> :: value;
    cout << BtoC << endl;

    // 检查int是否可以转换为float
    cout << "int to float: "
        << is_convertible<int, float> :: value
        << endl;

    // 检查int是否可以转换为const int
    cout << "int to const int: "
        << is_convertible<int, const int> :: value
        << endl;

    return 0;
}  

true
false
false
int to float: true
int to const int: true