Quick question

Hello all:

I have been working on a project in my spare time and have been unable to find the source of a linker error after a few hours.

First, the overloaded output operator in this class is throwing the following error when attempting to use the << operator:

Code:

1>Linking...
1>main.obj : 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 CayleyTable<int> &)" 
  (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@AAV?$CayleyTable@H@@@Z) 
  referenced in function _main
1>C:\Documents and Settings\asdfg\My Documents\Visual Studio 2005\Projects\test2\Debug\test2.exe : 
  fatal error LNK1120: 1 unresolved externals

This is with the following class:

Code:

template <class ItemType>
class CayleyTable
{
public:
	CayleyTable();
	CayleyTable(int NumOfElements);
	CayleyTable(CayleyTable<ItemType>& AnotherCayleyTable);

	void SetNumberOfElements(int n);
	void DefineCayleyTable(vector< vector<ItemType> >& ACayleyTable);

	int NumberOfElements();

	list< OrderedPair<int> >& FindIndices(ItemType Item);
	//Post: returns a list of ordered pairs of integers representing the indices in 
        //  which Item was found in the Cayley table

	ItemType ReturnIndex(int i, int j);
	//Post: returns the (i,j)th entry of the Cayley table

	friend ostream& operator << (ostream& out, CayleyTable<ItemType>& TheTable);

private:
	vector< vector<ItemType> > TheCayleyTable;
};

I defined the output operator for this class as follows:

Code:

template <class ItemType>	
ostream& operator << (ostream& out, CayleyTable<ItemType>& TheTable)
{
	for (int i = 0; i < TheTable.TheCayleyTable.size(); i++)
	{
		for (int j = 0; j < TheTable.TheCayleyTable.size(); j++)
		{
			out << TheTable.TheCayleyTable[i][j] << "  ";
		}
		out << endl;
	}

	return out;
}

Thanks for any help!

Put your template operator << in a header and don't prototype it and see if that works. If it isn't already, of course.

Did you put the implementation of this operator in a header file, as is necessary for templates?

Did you put your output operator in the header file? It needs to be included when you compile the source using the template.

--
Mats

Yes, all of the code associated with the class is in CayleyTable.h

It appears that you might need to declare the friend as this:

Code:

    template <class T>
	friend ostream& operator << (ostream& out, CayleyTable<T>& TheTable);

It seems that the class template typename doesn't apply to the declaration of a free friend function. (Compiler warns about declaring a non-templated function otherwise.)

Originally Posted by anon

It appears that you might need to declare the friend as this:

Code:

    template <class T>
	friend ostream& operator << (ostream& out, CayleyTable<T>& TheTable);

It seems that the class template typename doesn't apply to the declaration of a free friend function. (Compiler warns about declaring a non-templated function otherwise.)

Thanks, that did it.

Time for some sleep now...