Class template friend operators

[Catfish4]

The code below doesn't compile.
I would like to understand why and how to fix it.
Thank you.

Two things to clear up:
1) I know x is going to be garbage.
2) I know that it doesn't help that I used the same type name label ElementType.

#include <iostream>
#include <ostream>

template <typename ElementType>
class Example
{
private:
    ElementType x;

template <typename ElementType>
friend std::ostream & operator << (std::ostream &, const Example &);
};

template <typename ElementType>
std::ostream & operator << (std::ostream &os, const Example<ElementType> &e)
{
    os << e.x << '\n';
    return os;
}

int main()
{
    Example<int> e;
    std::cout << e << std::endl;
}

class_template_friends.cpp:10:11: error: declaration of 'class ElementType'
 template <typename ElementType>
           ^
class_template_friends.cpp:4:11: error:  shadows template parm 'class ElementType'
 template <typename ElementType>
           ^
class_template_friends.cpp: In instantiation of 'std::ostream& operator<<(std::ostream&, const Example<ElementType>&) [with ElementType = int; std::ostream = std::basic_ostream<char>]':
class_template_friends.cpp:24:18:   required from here
class_template_friends.cpp:8:17: error: 'int Example<int>::x' is private
     ElementType x;
                 ^
class_template_friends.cpp:17:8: error: within this context
     os << e.x << '\n';
        ^

[Daleth]

I saw a few threads about problems with friend templates when I searched the forum. But I remember seeing this one a little while back:
http://www.cplusplus.com/forum/general/110628/

The parashift page that Cubbi linked to also provides an explanation as to why friend function template prototypes can be an issue.

[Catfish4]

Thanks. The final version below works.

#include <iostream>
#include <ostream>

template <typename ElementType>
class Example
{
private:
    ElementType x;

template <typename Temp>
friend std::ostream & operator << (std::ostream &, const Example<Temp> &);
};

template <typename ElementType>
std::ostream & operator << (std::ostream &os, const Example<ElementType> &e)
{
    os << e.x << '\n';
    return os;
}

int main()
{
    Example<int> e;
    std::cout << e << std::endl;
}

[coder777]

The error tells you what's wrong: On line 10 you have a second template with the same name ElementType. Remove that. It should be fine for that error.

write the implementation of the operator<< inside the class. The reason is that only Example<int> is instantiated. For whatever reason the compiler sees the declaration of operator<< but not the implementation when it's outside the class and not used inside.