Ошибка вызова шаблонной функции - C++

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
const int Arsize = 10;
using namespace std;
template <class T>
int reduce(T *ar, int n);
//void show(const T & l) {cout << l << " ";}
int main()
{
    long arr[Arsize];
    cout << "Enter some digits:\n";
    for (int i = 0; i < Arsize; i++)
    {
        cout << "#" << i + 1 << ": ";
        cin >> arr[i];
    }
    cout << "You entered next: ";
    for (int i = 0; i < Arsize; i++)
    {
        cout << arr[i] << " ";
    }
 
    int num = reduce(arr, Arsize);
    cout << "\nModified array has " << num << " objects!\n";
 
    string str;
    cout << "Enter some string:\n";
    getline(cin, str);
    cout << "You entered next: " << str << endl;
    int n_str = str.size();
    int num_str = reduce(str, n_str);
    cout << "\nModified string has " << num_str << " objects!\n";
    return 0;
}
template <class T>
int reduce(T *ar, int n)
{
    vector<T> lst(ar, ar+n);
    sort(lst.begin(), lst.end());
    cout << "\nSorted array: ";
    for(auto x: lst) cout << x << " ";
 
    auto last_it = unique(lst.begin(), lst.end());
    cout << "\nArray after unique: ";
    for(auto x: lst) cout << x << " ";
 
    lst.erase(last_it, lst.end());
    cout << "\nArray after erase: ";
    for(auto x: lst) cout << x << " ";
 
    int num = lst.size();
    return num;
}

int num_str = reduce(str.c_str(), n_str);

template <class T>
size_t reduce(const T * ar, size_t n)