LNK2019 error when deriving from a template - c++

Question

I am trying to implement a PointArray class derived from a template. Here is what my hpp file for PointArray looks like:
#ifndef POINTARRAY_H
#define POINTARRAY_H
#include <iostream>
#include <sstream>
#include <stdio.h>
#include "Array.hpp"
using namespace Abhishek::CAD;
using namespace Abhishek::CONTAINERS;
namespace Abhishek
{
namespace CONTAINERS
{
class PointArray : public Array<Point>
{
public:
PointArray();//Default constrcutor.
PointArray(int size);//Constructor with size argument.
PointArray(const PointArray& arr);//Copy constructor.
~PointArray();//Destructor.
double Length() const;//Length function.
};
}
}
#endif
My cpp looks like this :
#include <iostream>
#include <sstream>
#include <stdio.h>
#include "PointArray.hpp"
using namespace Abhishek::CAD;
using namespace Abhishek::CONTAINERS;
namespace Abhishek
{
namespace CONTAINERS
{
//Default constructor.
PointArray::PointArray(): Array<Point>()
{
cout<<"Point arr default cons"<<endl;
}
//Constructor with size argument.
PointArray::PointArray(int size) : Array<Point>(size)
{
}
//Copy constructor.
PointArray::PointArray(const PointArray& arr) : Array<Point>(arr)
{
}
//destrcutor.
PointArray::~PointArray()
{
}
}
}
I get the LNK error :
error LNK2019: unresolved external symbol "public: __thiscall Abhishek::CONTAINERS::Array<class Abhishek::CAD::Point>::Array<class Abhishek::CAD::Point>(void)" (??0?$Array#VPoint#CAD#Abhishek###CONTAINERS#Abhishek##QAE#XZ) referenced in function "public: __thiscall Abhishek::CONTAINERS::PointArray::PointArray(void)" (??0PointArray#CONTAINERS#Abhishek##QAE#XZ)
1>PointArray.obj : error LNK2019: unresolved external symbol "public: __thiscall Abhishek::CONTAINERS::Array<class Abhishek::CAD::Point>::Array<class Abhishek::CAD::Point>(int)" (??0?$Array#VPoint#CAD#Abhishek###CONTAINERS#Abhishek##QAE#H#Z) referenced in function "public: __thiscall Abhishek::CONTAINERS::PointArray::PointArray(int)" (??0PointArray#CONTAINERS#Abhishek##QAE#H#Z)
1>PointArray.obj : error LNK2019: unresolved external symbol "public: __thiscall Abhishek::CONTAINERS::Array<class Abhishek::CAD::Point>::Array<class Abhishek::CAD::Point>(class Abhishek::CONTAINERS::Array<class Abhishek::CAD::Point> const &)" (??0?$Array#VPoint#CAD#Abhishek###CONTAINERS#Abhishek##QAE#ABV012##Z) referenced in function "public: __thiscall Abhishek::CONTAINERS::PointArray::PointArray(class Abhishek::CONTAINERS::PointArray const &)" (??0PointArray#CONTAINERS#Abhishek##QAE#ABV012##Z)
1>PointArray.obj : error LNK2019: unresolved external symbol "public: __thiscall Abhishek::CONTAINERS::Array<class Abhishek::CAD::Point>::~Array<class Abhishek::CAD::Point>(void)" (??1?$Array#VPoint#CAD#Abhishek###CONTAINERS#Abhishek##QAE#XZ) referenced in function __unwindfunclet$??0PointArray#CONTAINERS#Abhishek##QAE#XZ$0
1>C:\Users\Rambo\Documents\Level 6\Section 4.2b\Exercise 3\Debug\Exercise 3.exe : fatal error LNK1120: 4 unresolved externals
I dont understand why this could be happening. I included all the relevant header files and CPP files. If anyone can help I will really appreciate it.

Answer 1

You forgot to post the most relevant header: the one that declares the class template that causes the error. Almost certainly, that header declares the default constructor of the Array template:
Array();
but doesn't define it; either there is no definition, or you have a definition in a source file.
In either case, you'll get an error since templates must be defined in any translation unit that uses them. This means that you'll need to define the constructor (and any other member functions) in the header, to include them wherever they are used.
If that's not the problem, then please post the header so we can investigate further.