将trait類模闆用作模闆參數
【引例】 //SumFixedTraits類模闆
template <typename T>
struct SumFixedTraits;
template<>
struct SumFixedTraits<char>
{
using sumT = int;
static sumT initValue() { return 0; }
};
template<>
struct SumFixedTraits<int>
{
using sumT = __int64;
static sumT initValue() { return 0; }
};
template<>
struct SumFixedTraits<double>
{
using sumT = double;
static sumT initValue() { return 0.0; }
};
//----------------------
//funcsum函數模闆
template <typename T,typename U = SumFixedTraits<T> > //T
auto funcsum(const T* begin, const T* end)
{
using sumT = typename SumFixedTraits<T>::sumT;
sumT sum = SumFixedTraits<T>::initValue();
for (;;)
{
sum += (*begin);
if (begin == end)
break;
++begin;
}//end for
return sum;
}
【将trait類模闆用作模闆參數】 //funcsum函數模闆
template <typename T,typename U = SumFixedTraits<T> >
auto funcsum(const T* begin, const T* end)
{
//using sumT = typename SumFixedTraits<T>::sumT;
//sumT sum = SumFixedTraits<T>::initValue();
typename U::sumT sum = U::initValue();
for (;;)
{
sum += (*begin);
if (begin == end)
break;
++begin;
}//end for
return sum;
}
char mychararray[] = "abc";
cout << (int)(funcsum(&mychararray[0], &mychararray[2])) << endl;
template <typename T,typename U = SumFixedTraits<T> > //T = char ,U = SumFixedTraits<char>
auto funcsum(const T* begin, const T* end)
{
typename U::sumT sum = U::initValue();
//typename SumFixedTraits<char>::sumT sum = SumFixedTraits<char>::initValue();
//int sum = 0;
【改變char傳回值類型為__int64類型】 char mychararray[] = "abc";
cout << (int)(funcsum<char, SumFixedTraits<int> >(&mychararray[0], &mychararray[2])) << endl;