template<typename T>T c(T,T);
int main(void )
{int a=4;int b=12;
c(a,b);
     
}
 template <typename T>T c(T a,T b)
{
  cout<<a*b << endl;}

随便粘贴了某个码，区别很大
#include <iostream>
#include <algorithm>
using namespace std;

class even {
    int x;
public:
    even():x(0){}
    int operator()(){return x += 2;    }
};

int main( void )
{
   even tmp;
   cout << tmp() << ' ';
   cout << tmp() << endl;
}