C++ does not recognize generic type in implementation file [duplicate]

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• Why can templates only be implemented in the header file? 9 answers

I typed up this class in my VectorBag.h file and realized that I needed to separate the implementation into another file. I received no compilation errors before separation, but now the compiler does not seem to recognize that the functions in my implementation file are templated. I get these types of errors for every function in the implementation file.

error: ‘ItemType’ was not declared in this scope
 int VectorBag<ItemType>::getCurrentSize() const
           ^
error: template argument 1 is invalid
 int VectorBag<ItemType>::getCurrentSize() const

How do I make the program recognize these functions when they are in VectorBag.cpp instead of VectorBag.h? I have included all of the interface file and the first part of the implementation file. Thanks.

/* VectorBag.h */
#ifndef _VECTOR_BAG
#define _VECTOR_BAG


#include<vector>
#include"BagInterface.h"

using namespace std;

template<class ItemType>
class VectorBag : public BagInterface<ItemType>
{
public:

    int getCurrentSize() const;

    bool isEmpty() const;

    bool add(const ItemType& newEntry);

    bool remove(const ItemType& anEntry);

    void clear();

    int getFrequencyOf(const ItemType& anEntry) const;

    bool contains(const ItemType& anEntry) const;

    vector<ItemType> toVector() const;


   // New Bag Operations

   //vector<ItemType> operator+(vector<ItemType> right);


private:

    vector<ItemType> v;

};

#endif




/* VectorBag.cpp (partial) */

#include"VectorBag.h"

int VectorBag<ItemType>::getCurrentSize() const
{
        return v.size();
}