请问这里模板怎么没起作用？？？？

//===================================
//f1401.cpp
//定义和使用函数模板
//====================================
#include<iostream>
#include<string>
using namespace std;
template<typename T>
void swap(T& a,T& b)
{
    T temp=a;a=b;b=temp;
}//-----------------------------
int main()
{
    double dx=3.5,dy=5.6;
    int ix=6,iy=7,ia=303,ib=505;
    string s1="good",s2="better";
    cout<<"double dx="<<dx<<",    dy="<<dy<<endl;
    cout<<"int ix="<<ix<<",    iy="<<iy<<endl;
    cout<<"string s1="<<s1<<",    s2="<<s2<<endl;
    swap(dx,dy);
    swap(ix,iy);
    swap(ia,ib);
    swap(s1,s2);
    cout<<"after swap:\n";
    cout<<"double dx="<<dx<<",    dy="<<dy<<endl;
    cout<<"int ix="<<ix<<",    iy="<<iy<<endl;
    cout<<"string s1="<<s1<<",    s2="<<s2<<endl;
}