Templates and Unresolved Externals

[yohosuff]

I'm not sure why I am getting unresolved externals. These are the errors I get:

1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall Array<int,10>::~Array<int,10>(void)" (??1?$Array@H$09@@QAE@XZ) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "public: int __thiscall Array<int,10>::getSize(void)const " (?getSize@?$Array@H$09@@QBEHXZ) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall Array<int,10>::Array<int,10>(void)" (??0?$Array@H$09@@QAE@XZ) referenced in function _main
1>F:\Users\yohosuff\Desktop\C++ HTPE10\Debug\C++ HTPE10.exe : fatal error LNK1120: 3 unresolved externals

Here's the code:

#ifndef ARRAY_H
#define ARRAY_H
#include <iostream>
using std::ostream;
using std::istream;

template<typename T, int numberOfElements>
class Array
{
	friend ostream &operator<<( ostream &, const Array<T,numberOfElements> & );
	friend istream &operator>>( istream &, Array<T,numberOfElements> & );      
public:
	Array();
	~Array();          
	int getSize() const;
	const Array &operator=( const Array & );
	bool operator==( const Array & ) const;

	bool operator!=( const Array &right ) const                 
	{                                                           
		return ! ( *this == right );
	}                              
	
	T &operator[]( int );                                              
	
	T operator[]( int ) const;                          
private:
	int size; 
	T *ptr;
};
#endif

#include <iostream>
using std::cerr;
using std::cout;
using std::cin;
using std::endl;
#include <iomanip>
using std::setw;
#include <cstdlib>
using std::exit;

#include "Array.h" // Array class definition


template<typename T, int numberOfElements>
Array<T,numberOfElements>::Array()
{
	size = ( numberOfElements > 0 ? numberOfElements : 10 );
	ptr = new T[ size ];
	for ( int i = 0; i < size; i++ )
		ptr[ i ] = 0; 
}


template<typename T, int numberOfElements>
Array<T,numberOfElements>::~Array()
{
	delete [] ptr;
} 

template<typename T, int numberOfElements>
int Array<T,numberOfElements>::getSize() const
{
	return size;
}

template<typename T, int numberOfElements>
const Array<T,numberOfElements> &Array<T,numberOfElements>::operator=( const Array<T,numberOfElements> &right )
{
	if ( &right != this ) 
	{
		
		if ( size != right.size )
		{
			delete [] ptr;
			size = right.size; 
			ptr = new T[ size ]; 
		} 
		for ( int i = 0; i < size; i++ )
			ptr[ i ] = right.ptr[ i ];
	}
	return *this;
} 

template<typename T, int numberOfElements>
bool Array<T, numberOfElements>::operator==( const Array<T,numberOfElements> &right ) const
{
	if ( size != right.size )
		return false; 
	for ( int i = 0; i < size; i++ )
		if ( ptr[ i ] != right.ptr[ i ] )
			return false;
	return true;
}

template<typename T, int numberOfElements>
T &Array<T, numberOfElements>::operator[]( int subscript )
{
	if ( subscript < 0 || subscript >= size )
	{
		cerr << "\nError: Subscript " << subscript
			<< " out of range" << endl;
		exit( 1 ); 
	} 
	return ptr[ subscript ];
}


template<typename T, int numberOfElements>
T Array<T,numberOfElements>::operator[]( int subscript ) const
{

	if ( subscript < 0 || subscript >= size )
	{
		cerr << "\nError: Subscript " << subscript
			<< " out of range" << endl;
		exit( 1 );
	}

	return ptr[ subscript ]; 
}


template<typename T, int numberOfElements>
istream &operator>>( istream &input, Array<T,numberOfElements> &a )
{
	for ( int i = 0; i < a.size; i++ )
		input >> a.ptr[ i ];

	return input; 
} 


template<typename T, int numberOfElements>
ostream &operator<<( ostream &output, const Array<T,numberOfElements> &a )
{
	int i;

	for ( i = 0; i < a.size; i++ )
	{
		output << setw( 12 ) << a.ptr[ i ];

		if ( ( i + 1 ) % 4 == 0 ) 
			output << endl;
	}

	if ( i % 4 != 0 ) 
		output << endl;

	return output;
}

#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
#include <ctime>
#include <vector>

using namespace std;

#include "Array.h"

int main()
{

	//14.7
	Array<int,10> a;
	a.getSize();

	//********************
	cout << "\nProgram Execution Complete\n";
	system("PAUSE");
	return 0;
}

Any help would be appreciated!

[ZuK]

You have to move the code from your template implementatation file into the header or #include it from the header.
Reason: at the point of instantiation of a template the compiler has to be able to see the implementation.
Search the forum for a better explaination. This problem comes up rather frequently.
Kurt

[potatoCode]

and here's the link to Zuk's explaination.
Why do I get linker errors when I use template friends?

[yohosuff]

Thanks for the tips, I'll give it a shot.

[yohosuff]

Awesome! Placing the implementation of the class in the header file worked! And, potatoCode, that link you provided was very helpful. Very helpful indeed. Kudos!