Unique_copy不返回预期输出

Question

I have this simple code, i know i must be doing some silly mistake :

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<iterator>
using namespace std;

int main()
{
vector<string> coll{"one", "two", "two", "three", "four", "one"};
vector<string> col2(coll.size(), "");
unique_copy(coll.cbegin(), coll.cend(), col2.begin());
for(const auto& ele : col2)
    cout<<" - "<<ele;
cout<<endl;
return 0;
}

Output - - one - two - three - four - one -

I was expecting :- - one - two - three - four - -

What am i missing?

EDIT: As pointed out in aswer - Damn, i was missing the definition of unique_copy itself.

Is there any function to do what i expectecd (delete unique elements irrespective of adjacency), other than inserting them in ordered set or sorting before unique copy as i want to keep the ordering.

Answer 1

std::unique_copy :

Copies the elements from the range [first, last) , to another range beginning at d_first in such a way that there are no consecutive equal elements.

one is not consecutive in your case.

Try:

vector<string> coll{"one", "one", "two", "two", "three", "four"};

you will find the output as

- one - two - three - four -  -