C++:using template containers in function

marktsang

hey all,
quick question is this possible

i want to use a template function that takes a list or vector container of some type, lets say a vector<int> and list<int> as the parameter

template <class container>
void printContents(container c)
{
	container::iterator iter = c.begin();
	while (iter != c.end())
	{
		cout << *iter << endl;
		++iter;
	}
}

int main()
{
	vector<int> intVec;
	
	intVec.push_back(1);
	intVec.push_back(2);
	intVec.push_back(3);
	
	printContents(intVec);
	
	list<int> intlist;
	
	intlist.push_back(1);
	intlist.push_back(2);
	intlist.push_back(3);
	
	printContents(intlist)
	
	return 1;
}

is this possible????

thanks

Tobias Greeshman

Add this to the start of the template function (as first two statements in body of funtion) and it'll work.

typedef typename container::iterator cont_iter;
    cont_iter iter = c.begin();

The reason this fails is because the "container::iterator" is a dependent type and the C++ compiler knows nothing about this type at compile time, or even that it is a nested type, so we need to tell the compiler it's one.

In short: "if your type is qualified by a template type parameter, you must use typename."

You generally shouldn't need typedef, but g++ 4.2 see to insist.

marktsang

thats great!!
worked fine.

thanks
mark

marktsang

hey,
on a related note how would i make the return of that function be an iterator of the con types class??

template <class container, class iter>
iter printContents(container c)
{
	container::iterator iter = c.begin();
	while (iter != c.end())
	{
		cout << *iter << endl;
		++iter;
	}
        return c.begin();
}

int main()
{
	vector<int> intVec;
	
	intVec.push_back(1);
	intVec.push_back(2);
	intVec.push_back(3);
	
	printContents(intVec);
	
	list<int> intlist;
	
	intlist.push_back(1);
	intlist.push_back(2);
	intlist.push_back(3);
	
	printContents(intlist)
	
	return 1;
}

Tobias Greeshman

I'm not 100% sure how to go about this, my template programming skills are very limited.

If you ask on the comp.lang.c++ newsgroup (via groups.google.com) you're sure to get an answer, the guys on there really know there template code.

marktsang

thanks alot for having a look at it -
i will have a look at comp.lang.c++ newsgroup

cheers,
mark