未知容器，矢量或数组c ++的大小

Question

I try to build a template function that gets 2 iterators( begin and end ) of either a vector or an array (this must be unknown container passed to function).

1. I want that the function will check for the size of the container passed to it. My problems are: if begin iterator equals end iterator does it mean 0 or 1 elements inside container? How can I decalare some universal size type ?

2. If I want to sort the unknown container by passing iterators to sort function is that becomes a problem? I have some feeling that it won't work.

This is my draft of the template function:

    template<class P, class T>
    T my_func(P beg, P end)
    {
       typedef typename ??? container_size;
       if (beg == end)//first problem to determine if contains 0 or 1 
                         elements 

       throw domain_error("some message if 0 elements");

       sort(beg, end);// scond problem

    }

Answer 1

1. I want that the function will check for the size of the container passed to it. My problems are: if begin iterator equals end iterator does it mean 0 or 1 elements inside container? How can I decalare some universal size type ?

You should use std::distance for that.

2. If I want to sort the unknown container by passing iterators to sort function is that becomes a problem? I have some feeling that it won't work.

It would work, provided the iterators are RandomAccessIterators and the value type is swappable

---

So, your code could be:

template<class P, class T>
T my_func(P first, P last)
{
   if(first == last) // No elements within the range
        throw domain_error("some message if 0 elements");

   //Number of Elements within the range
   auto container_size = std::distance(first, last);

   std::sort(first, last);

   return ...;
}

If my guess is correct, that the template parameter T is supposed to be the value type of the iterator, you can obtain it using std::iterator_traits<T>::value_type