Error calling the overloaded istream operator in a Template Class - c++

Question

I want to overload the ">>" operator in a template class, but when I am trying to write someting into a vector I am getting some errors.
This is a part of my Vector function:
#include <iostream>
template<typename T>
class Vector
{
public:
T operator[](const int& i);
template <T> friend
std::ostream& operator<<(std::ostream& out, const Vector &v);
template <T> friend
std::istream& operator>>(std::istream& in, Vector<T> &v);
};
template<typename T>
std::istream& operator>>(std::istream& in, Vector<T> &v) {
for(int i =0; i < v.getSize(); i++) {
in >> v[i];
}
}
I used this test to write into a vector:
int main {
Vector<int> v1(5);
cin >> v1;
}
This is the error:
Vector.h: In function ‘std::istream& operator>>(std::istream&, Vector<T>&) [with T = int, std::istream = std::basic_istream<char>]’:
testVector.cpp:9:9: instantiated from here
Vector.h:94:3: error: ambiguous overload for ‘operator>>’ in ‘in >> (& v)->Vector<T>::operator[] [with T = int]((*(const int*)(& i)))’
Vector.h:94:3: note: candidates are:
/usr/include/c++/4.6/istream:122:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT,
This is a part of my code. If I am using in a test function only something like this, it compiles:
Vector<int> v1.
cout << v1.getSize();
Update:
I've modified the >> operator overloading definition like this:
template<typename T> std::istream& operator>>(std::istream& in, Vector<T> &v) {
T tmp;
for(int i =0; i < v.getSize(); i++) {
in >> tmp;
v[i] = tmp;
}
}
This is the definition of the operator[]:
template<typename T> T Vector<T>::operator[](const int& i) {
return elements[i];
}
I get this error:
Vector.h:96:3: error: lvalue required as left operand of assignment
How should I overwrite the >> operator?
Thanks.

Answer 1

These lines:
template <T> friend std::ostream& ...
template <T> friend std::istream& ...
The template argument should be a type. As you've written it, it takes an object of said type.
template<typename U> friend std::ostream& ...
template<typename U> friend std::istream& ...
And you didn't specify a template argument here:
Vector v1(5);
^

Answer 2

Your problem has nothing to do with stream overloading:
You have two constructors with the same argument int. The names of the constructor doesn't matter main thing is the type. So two Vector<T>(int) will give you error overloading error.
You do not have an overloaded subscript operator (operator[]), set it up to fix the main problem
as 0x499602D2 mentioned, change the friend classes to the correct form because you will get error "accessing private member variable of class Vector" if you tried to use private members. In your scenario, you are accessing public members, so you might not even need friending the stream overloading. Read about friend here. So, ask yourself a question? "Will the stream operator function access the private member of class Vector?" If yes, use friend; otherwise remove it from your class declaration.
Remove the def from the source code. We understand that its coming from a source file.
The test program doesn't work because you haven't specified which template parameter you are using.
EDIT: added link for (3) to read about friendship