在函数中传递ifstream迭代器

Question

Why is this code working? e iterator isn't point-assigned to anything. How is implied that the function continues until the end of the fstream?

#include <vector>
#include <iostream>
#include <list>
#include <fstream>
#include <string>
#include <iterator>

using namespace std;

template<typename InputIterator>
void printRange(InputIterator first, InputIterator last)
{
    while (first != last)
    {
        std::cout << *first << endl;
        ++first;
    }
}
int main()
{
    vector<int> v = { 11, 24, 541 };
    printRange(v.begin(), v.end());
    cout << endl;
    list<double> lst = { 11.88, 21.4, 541.9 };
    printRange(lst.begin(), lst.end());
    cout << endl;
    ifstream ifs{ "strings.txt" };
    istream_iterator<string> i(ifs);
    istream_iterator<string> e;
    printRange(i, e);
}

strings.txt

coding c++

Answer 1

The variable e is default constructed, so the 0-argument constructor is called. And from the documentation :

constexpr istream_iterator();

Constructs the end-of-stream iterator. This constructor is constexpr if std::is_trivially_default_constructible_v<T> is true.

So default constructing an istream_iterator constructs the end-of-stream iterator, which is exactly the value you need.