C++ 函数模板示例 2 (配合decltype)

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <string.h>
#include <new>

using std::cout;
using std::cin;
using std::endl;
using std::setw;

template<class T1, class T2>
auto product(T1 v1[], T2 v2[], size_t count) -> decltype(v1[0]*v2[0])
{
decltype(v1[0]*v2[0]) sum(0);
for(size_t i=0;i<count;i++) sum += v1[i]*v2[i];
return sum;
}

int main(int argc,_TCHAR* argv[])
{
double x[] = {100.5,99.5,88.7,77.8};
short y[] = {3,4,5,6};
long z[] = {11L,22L,33L,44L};

size_t n=4;

cout <<"result type is " <<typeid(product(x,y,n)).name()<<endl;
cout<<"result is "<<product(x,y,n)<<endl;

cout <<"result type is " <<typeid(product(z,y,n)).name()<<endl;
cout<<"result is "<<product(z,y,n)<<endl;

return 0;
}

</pre><pre name="code" class="cpp">上面代码的运行结果是：