Thread: 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!

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

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...