iterators as parameters in template functions

[mzimmers]

Hi -

I'm trying to create a template function. Here's the .h file:

#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

template <class T> int getVectort(ifstream & s,
				   long	nbrCells,
				   typename vector<T>::iterator a);

And here's the .cpp file:

using namespace std;

template <class T> int	getVectort(ifstream& s,
				  long nbrCells,
				  typename vector<T>::iterator iter)
{
	int		rc = 0;
	int32_t	temp;
	for (int i = 0; i < nbrCells; i++)
	{
		s >> hex >> temp;
		*iter++ = temp;
	}
	if (s.fail())
		rc = 1;
	return rc;
}

They compile OK.

But...when I try to use one, like this:

	vector<int32_t>::iterator iter;
.
.
.
		rc = getVectort(fileIn, DEMOD_NBR_INPUTS, iter);

I get this build error:

error: no matching function for call to 'getVectort(std::ifstream&, const long int&, __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >&)'

What am I doing wrong? Thanks.

[Peter87]

templates should be defined in the header file.

[mzimmers]

Still not compiling; thanks for the reminder on that, though. I combined them into one .h file and removed the .cpp file from my configuration. I appear to be getting the same error:

error: no matching function for call to 'getVectort(std::ifstream&, const long int&, __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >&)'

Is there something wrong with the way I defined the template parameter?

EDIT:

Just to experiment, I removed all arguments except for the iterator from the function definition, and the call to it. Effectively the same error message.

Any ideas? Thanks.

[DarioDigiuni]

You're trying to use automatic type deduction, but it won't work like that (it can't deduce the template argument of std::vector<T> !).

I'd suggest the following

template <class Iterator>
int getVectort(/* whatv... */  Iterator a)
{
typedef typename Iterator::value_type T;
// ...
}

So you also have the value type. Every iterator must have a value_type, otherwise it's not an iterator.

EDIT: added typename

[DarioDigiuni]

Or you can of course use you code and just specify the template argument

vector<int32_t>::iterator iter;
rc = getVectort<int32_t>(fileIn, DEMOD_NBR_INPUTS, iter);

[mzimmers]

I don't think I understand your first example, Dario. If it's not too much trouble, could you elaborate?

I already tried the second example you gave, and it doesn't change the error message.

Thanks.

[mzimmers]

Solved...cockpit error.

[DarioDigiuni]

Hey.

It means you'd have to call the function like this

std::vector<int32_t> vec(n,1);
rc = getVectort(/*whatv...*/ vec.begin());

And the body of your function doesn't change, except when you have to explicitly use the typename T (like during instantiation). However, I also saw that in your original code you set

*iter++ = temp;

Where temp is an int32_t regardless of the template parameter type. Seems wrong.

[bluecoder]

Where temp is an int32_t regardless of the template parameter type. Seems wrong.

this statement seems confusing to me please can you elobrate
And also i suppose the return type you have put is int ... which should be T .
correct me if i am wrong.
Thanks in advance .