STL std::find() C++

Question

In the below code I declared a vector as {1,2,3,4,5} .

Using the STL std::find() , I am trying to find 5 in the vector ranging from arr.begin() to arr.end()-1 or arr.begin() to arr.begin()+4 which is the same range from 1 to 4 .

But here for both, iterators are return pointing to 5 . Why is that since the range is only from 1 to 4 ?

#include <iostream>
#include <vector>
#include <array>
#include <algorithm>
using namespace std;

int main () {
    vector<int> arr {1,2,3,4,5};
    // TEST
    for_each(arr.begin(), arr.begin()+4, [](const int &x) { cerr << x << " "; }); cerr << endl;
    for_each(arr.begin(), arr.end()-1, [](const int &x) { cerr << x << " "; }); cerr << endl;

    auto it1 {std::find(arr.begin(), arr.begin()+4, 5)};
    auto it2 {std::find(arr.begin(), arr.end()-1, 5)};

    if (it1 != arr.end())
        cout << *it1 << " Found!" << endl;
    else
        cout << "NOT Found!" << endl;

    if (it2 != arr.end())
        cout << *it2 << " Found!" << endl;
    else
        cout << "NOT Found!" << endl;
    return 0;
}

OUTPUT:

1 2 3 4 
1 2 3 4 
5 Found!
5 Found!

Answer 1

std::find just returns the iterator passed as the 2nd argument when the element is not found. So it returns the iterators as arr.begin()+4 or arr.end()-1 in your code.

You shouldn't compare it with std::end , eg

if (it1 != arr.begin()+4)
    cout << *it1 << " Found!" << endl;
else
    cout << "NOT Found!" << endl;

if (it2 != arr.end()-1)
    cout << *it2 << " Found!" << endl;
else
    cout << "NOT Found!" << endl;

Answer 2

It is because if std:find does not find the requested value (as it occurs here), it returns the end iterator you give to it (not the end iterator of the full vector), which in this case points to the element you are looking for.