c++ template minimum function

Question

I want implement a function in c++ which returns the minimum of an array of any type. My code for now looks like this:

main.cpp:

#include <iostream>
#include <bits/unique_ptr.h>
#include "MathHelper.h"

using namespace std;

int main() {
    std::array<int, 3> myarray = {10,20,30};
    int i = MathHelper::minimum(myarray);
    printf("%d\n", i);
    return 0;
}

MathHelper.h:

#ifndef OPTIMIERUNG_MATHHELPER_H
#define OPTIMIERUNG_MATHHELPER_H


#include <stddef.h>
#include <array>

class MathHelper {
public:
    template <typename T, size_t SIZE>
     static T minimum(std::array<T, SIZE>& a);

};


#endif //OPTIMIERUNG_MATHHELPER_H

MathHelper.cpp:

#include "MathHelper.h"

template<typename T, size_t SIZE>
T MathHelper::minimum(std::array<T, SIZE> &a) {
    int minimum = a[0];
    if(SIZE>0){
        for(size_t i=1;i<SIZE;i++){
            if(a[i] < minimum){
                minimum = a[i];
            }
        }
    }
    return minimum;
}

executing this program results into following exception:

undefined reference to `int MathHelper::minimum<int, 3ul>(std::array<int, 3ul>&)'

[There's already such a function in the standard library](http://en.cppreference.com/w/cpp/algorithm/min_element) — Some programmer dude, Oct 30 '15 at 11:48
As for your problem, where do you define the function? Where do you call it? Can you please create a [Minimal, Complete, and Verifiable Example](http://stackoverflow.com/help/mcve) and show us? — Some programmer dude, Oct 30 '15 at 11:49
I have to do this for a project for university where I have to do it myself. I edited the example to provide a minimal and complete example — Finkes, Oct 30 '15 at 12:04
Your function seems to work fine. [Example](http://coliru.stacked-crooked.com/a/42367be0ea03d517) — rozina, Oct 30 '15 at 12:05
Template functions need to be implemented in the header not cpp. — rozina, Oct 30 '15 at 12:06
["Why can templates only be implemented in the header file?"](http://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file) — Some programmer dude, Oct 30 '15 at 12:07
interesting. Putting it into the header is indeed the solution thanks. How can I mark your comment as correct answer? — Finkes, Oct 30 '15 at 12:12
If you accept arrays of T, don't use int as a temporary variable holding the minimum. Use T. — Tadeusz Kopec for Ukraine, Oct 30 '15 at 12:32
And if `SIZE == 0`, then `a[0]`is already out of bound access. — Jarod42, Oct 30 '15 at 13:06

score 0 · Accepted Answer · answered Oct 30 '15 at 12:21

0

As rozina and Joachim Pileborg commented template functions have to be implemented inside the header.

answered Oct 30 '15 at 12:21

Finkes

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c++ template minimum function

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