I get a linking error (LINK 2019) when I try to augment a class with template - c++

Question

I'm trying to build a simple heap data structure for practice. When I build the version for double it works fine.
class heapt {
public:
heapt();
heapt(std::initializer_list<double> lst);
void print_heapt();
private:
int size;
int length;
double* elem; //points to root
};
Its constructors works perfectly and the heap is printed as it should. But when I try to generalize it with
template< typename Elem>
as:
template<typename Elem>
class heapt {
public:
heapt();
heapt(std::initializer_list<Elem> lst);
void print_heapt();
private:
int size;
int length;
Elem* elem; //points to root
};
for the class definition and as:
template<typename Elem>
heapt<Elem>::heapt(std::initializer_list<Elem> lst) :
size{ static_cast<int>(lst.size()) },
elem{new Elem[lst.size()]}
{
std::copy(lst.begin(), lst.end(), elem);//Now heaptify elem
build_heapt(elem, lst.size());
}
for one of the constructors used in the main function.
I get two linking errors:
LNK2019 unresolved external symbol "public: void __thiscall heapt::print_heapt(void)" (?print_heapt#?$heapt#H##QAEXXZ) referenced in function _main
LNK2019 unresolved external symbol "public: __thiscall heapt::heapt(class std::initializer_list)" (??0?$heapt#H##QAE#V?$initializer_list#H#std###Z) referenced in function _main
The main function is:
{
heapt<int> hh{ 27,12,3,13,2,4,14,5 };
std::cout << "Hello" << '\n';
hh.print_heapt();
}
EDIT: The heapt class is in the "heap.h" file and the definition for the constructor heapt<Elem>::heapt(std::initializer_list<Elem> lst) is in the "heap.cpp" class, which has #include"heap.h" as a header file. The int main function is in a file named "InSo.cpp", which also has #include"heap.h" as a header file.

Answer 1

In your templated class declaration you are using heapt(std::initializer_list<double> lst); but in your definition you are using std::initializer_list<Elem>. You should change the declaration to heapt(std::initializer_list<Elem> lst);
You are still missing definitions for print_heapt and build_heapt but otherwise it should compile.
EDIT: In light of you clarifying how your source files are set up, see WhozCraig's comment on your initial post. You can either include the definition of the templated class functions in a heap.hpp file, for example, and include it at the end of your heap.h, or just put them all together in one file, e.g.
// heap.h
#ifndef HEAP_H
#define HEAP_H
#include <initializer_list>
template<typename Elem>
class heapt {
public:
heapt();
heapt(std::initializer_list<Elem> lst);
void print_heapt();
private:
int size;
int length;
Elem* elem; //points to root
};
#include "heap.hpp"
#endif
//heap.hpp
#ifndef HEAP_HPP
#define HEAP_HPP
#include "heap.h"
#include <algorithm>
template<typename Elem>
heapt<Elem>::heapt(std::initializer_list<Elem> lst) :
size{ static_cast<int>(lst.size()) },
elem{ new Elem[lst.size()] }
{
std::copy(lst.begin(), lst.end(), elem);//Now heaptify elem
//build_heapt(elem, lst.size());
}
#endif