C++编译期判断是否能够转型

时间:2020-12-25 00:32:28
#include <iostream>
#include <vector>
using namespace std; template<class T,class U>
class Conversion
{
private:
typedef char Small;
class Big{char dummy[];};
static Small test(U);
static Big test(...);
static T makeT();
public:
enum{ exists =
sizeof(test(makeT()))==sizeof(Small) };
enum{ exists2Way =
exists && Conversion<U,T>::exists};
enum{
sameType=false};
}; template<class T>
class Conversion<T,T>
{
public:
enum{exists=,exists2Way=,sameType=};
}; #define SUPERSUBCLASS(T,U)\
(Conversion<const U*,const T*>::exists && \
!Conversion<const T*,const void*>::sameType)
#define SUPERSUBCLASS_STRICT(T,U)\
(SUPERSUBCLASS(T,U) && \
!Conversion<const T,const U>::sameType)
class Shape
{
public:
virtual void display()
{
cout<<"Shape"<<endl;
}
}; class Circle:public Shape
{
public:
virtual void display()
{
cout<<"Circle()"<<endl;
}
}; int _tmain(int argc, _TCHAR* argv[])
{
cout<<Conversion<double,int>::exists<<endl;
cout<<SUPERSUBCLASS(Shape,Circle)<<endl;
cout<<SUPERSUBCLASS_STRICT(Shape,Circle)<<endl;
return ;
}