Q:

c++ failed to specialize function template 'iterator_traits'

im trying to compile a school assignment but im getting an error, and since there is no qualified teacher available at uni at this hour, i've come here for help.
im getting a error stating: "Error  C2893   Failed to specialize function template 'iterator_traits<_Iter>::difference_type std::distance(_InIt,_InIt)'" line 22
i have no clue as to why this error occurs.
code:
#pragma once
// ttt.h

#ifndef TTT_H
#define TTT_H

#include <tuple>
#include <array>
#include <vector>
#include <ctime>
#include <random>
#include <iterator>
#include <iostream>

enum class Player { X, O, None };
using Move = int;
using State = std::array<Player, 9>;

// used to get a random element from a container
template<typename Iter, typename RandomGenerator>
Iter select_randomly(Iter start, Iter end, RandomGenerator& g) {
    std::uniform_int_distribution<> dis(0, std::distance(start, end) - 1);
    std::advance(start, dis(g));
    return start;
}

template<typename Iter>
Iter select_randomly(Iter start, Iter end) {
    static std::random_device rd;
    static std::mt19937 gen(rd());
    return select_randomly(start, end, gen);
}

std::ostream &operator<<(std::ostream &os, const State &state);
std::ostream &operator<<(std::ostream &os, const Player &player);

Player getCurrentPlayer(const State &state);
State doMove(const State &state, const Move &m);
Player getWinner(const State &state);
std::vector<Move> getMoves(const State &state);

#endif // TTT_H

function call":
State mcTrial(const State &board)
{
    State currentBoard = board;
    std::vector<Move> possibleMoves = getMoves(currentBoard);
    while (possibleMoves.size() > 0) {
        int move = select_randomly(0, (int)possibleMoves.size() -1);
        Move m = possibleMoves[move];
        currentBoard = doMove(currentBoard, m);
        possibleMoves = getMoves(currentBoard);
    }
return currentBoard;
}

A:

You should pass iterators to select_randomly, not indexes. Here is the proper function call: std::vector<Move>::iterator it = select_randomly(possibleMoves.begin(), possibleMoves.end()); To learn more about iterators visit http://www.cprogramming.com/tutorial/stl/iterators.html

