Hi . What is the problem of this :

template < typename B >
ostream &operator << ( ostream &out, const Array < B > &a )

The compiler say "Link error" and ...

>The compiler say "Link error" and ...
And what?
Could you please post the whole error message (plus code), and what's Array ?

My Program :

#ifndef ARRAY_H
#define ARRAY_H

#include <iostream>
using namespace std;

template < typename B >
class Array
{
	friend ostream &operator << ( ostream &, const Array < B > & );
	friend istream &operator >> ( istream &, Array < B > & );
public:
	Array ( int = 10 );
	Array ( const Array & );
	~Array ( );
	int getSize ( ) const;

	const B &operator = ( const Array & );
	bool operator == ( const Array & ) const;

	bool operator != ( const Array &right ) const
	{
		return ! ( *this == right );
	}

	B &operator [ ] ( int );
	B operator [ ] ( int ) const;
private:
	int size;
	B *ptr;
};

#endif
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include "Array.h"

using namespace std;

template < typename B >
Array < B >::Array ( int arraySize )
{
	size = ( arraySize > 0 ? arraySize : 10 );
	ptr = new B [ size ];

	for ( int i = 0; i < size; i++ )
		ptr [ i ] = 0;
}

template < typename B >
Array < B >::Array ( const Array &arrayToCopy ) : size ( arrayToCopy.size )
{
	ptr = new B [ size ];

	for ( int i = 0; i < size; i++ )
		ptr [ i ] = arrayToCopy.ptr [ i ];
}

template < typename B >
Array < B >::~Array ( )
{
	delete [ ] ptr;
}

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

template < typename B >
const B &Array < B >::operator = ( const Array &right )
{
	if ( &right != this )
	{
		if ( size != right.size )
		{
			delete [ ] ptr;
			size = right.size;
			ptr = new B [ size ];
		}

		for ( int i = 0; i < size; i++ )
			ptr [ i ] = right.ptr [ i ];
	}

	return *this;
}

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

	return ptr [ subscript ];
}

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

	return ptr [ subscript ];
}

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

	return input;
}

template < typename B >
ostream &operator << ( ostream &output, const Array < B > &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 "Array.h"

using namespace std;

int main ( )
{
	Array < int > as ( 5 );
	cout << "Size of array is : " << as.getSize ( ) << "\nArray contents : " << as;

	Array < double > ad ( 6 );
	cout << "\nSize of array is : " << ad.getSize ( ) << "\nArray contents : " << ad;

	system ( "pause" );

	return 0;
}

And Error :

Error 1 error LNK2019: unresolved external symbol "public: __thiscall Array<int>::~Array<int>(void)" (??1?$Array@H@@QAE@XZ) referenced in function _main main.obj
Error 2 error LNK2019: unresolved external symbol "public: __thiscall Array<double>::~Array<double>(void)" (??1?$Array@N@@QAE@XZ) referenced in function _main main.obj
Error 3 error LNK2019: unresolved external symbol "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class Array<double> const &)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@ABV?$Array@N@@@Z) referenced in function _main main.obj
Error 4 error LNK2019: unresolved external symbol "public: int __thiscall Array<double>::getSize(void)const " (?getSize@?$Array@N@@QBEHXZ) referenced in function _main main.obj
Error 5 error LNK2019: unresolved external symbol "public: __thiscall Array<double>::Array<double>(int)" (??0?$Array@N@@QAE@H@Z) referenced in function _main main.obj
Error 6 error LNK2019: unresolved external symbol "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class Array<int> const &)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@ABV?$Array@H@@@Z) referenced in function _main main.obj
Error 7 error LNK2019: unresolved external symbol "public: int __thiscall Array<int>::getSize(void)const " (?getSize@?$Array@H@@QBEHXZ) referenced in function _main main.obj
Error 8 error LNK2019: unresolved external symbol "public: __thiscall Array<int>::Array<int>(int)" (??0?$Array@H@@QAE@H@Z) referenced in function _main main.obj
Error 9 fatal error LNK1120: 8 unresolved externals C:\Documents and Settings\Administrator\My Documents\Visual Studio 2008\Projects\Array\Debug\Array.exe

Could you please post using code tags?
Is it that difficult? Just click the # button (and past your code in between the tags).
Read also this and this :)

You failed to write the Array class's constructor implementation code.

#ifndef ARRAY_H
#define ARRAY_H

#include <iostream>
using namespace std;

template < typename B >
class Array
{
	friend ostream &operator << ( ostream &, const Array < B > & );
	friend istream &operator >> ( istream &, Array < B > & );
public:
	Array ( int x = 10 )

       {
             color = x;
             ptr = 0;
       }
	Array ( const Array & a )

       {
             color = a.color;
             ptr = a.ptr;
       }

	~Array ( );
	int getSize ( ) const;

	const B &operator = ( const Array & );
	bool operator == ( const Array & ) const;

	bool operator != ( const Array &right ) const
	{
		return ! ( *this == right );
	}

	B &operator [ ] ( int );
	B operator [ ] ( int ) const;
private:
	int size;
	B *ptr;
};

#endif

Look in your textbook for class constructors. What I posted is called inline code. Or you can find more info online.

That header file has similar problems with all the other methods of that class. You have to write code that implements all those methods, or get the code from who ever you got that header file.

This article has been dead for over six months. Start a new discussion instead.