我正在学校的一个小班级模板实验室中工作，我的代码无法编译，这给了我一个无法解析的外部符号

Question

I am getting an unresolved external error when compiling the code, and i cannot figure out what the issue is. I am pretty positive that the template and functions are being used and created according to the assignment, but i just cannot get it to compile. Any help on the matter would be greatly appreciated .H

    #pragma once
    #include<iostream>
    using namespace std;
    template <class P>

    class Pair
    {
    private:
        P firstLetter;
        P secondLetter;

    public:
        Pair(const P&, const P&);

        P getSecondLetter();
        P getFirstLetter();
    };

    template <class P>
    P Pair<P>::getFirstLetter()
    {
        return firstLetter;
    }

    template <class P>
    P Pair<P>::getSecondLetter()
    {
        return secondLetter;
    }

Main: #include

    #include "Pair.h"

    using namespace std;


    int main()
    {
        Pair<char> letters('a', 'd');
        cout << "\nThe first letter is: " << letters.getFirstLetter();
        cout << "\nThe second letter is: " << letters.getSecondLetter();

        cout << endl;
        system("Pause");
        return 0;
    }

Answer 1

Almost there. Just add the constructor (this is probably the one you wanted)

template <class P>
Pair<P>::Pair(const P &p1, const P &p2) : firstLetter(p1), secondLetter(p2) { }

For a finished version something like this:

#pragma once
#include<iostream>
using namespace std;
template <class P>

class Pair
{
private:
    P firstLetter;
    P secondLetter;

public:
    Pair(const P&, const P&);

    P getSecondLetter();
    P getFirstLetter();
};

template <class P>
Pair<P>::Pair(const P &p1, const P &p2) : firstLetter(p1), secondLetter(p2) { }

template <class P>
P Pair<P>::getFirstLetter()
{
    return firstLetter;
}

template <class P>
P Pair<P>::getSecondLetter()
{
    return secondLetter;
}