template friend functions of template class

Question

I have the following template class and template function which intends to access the class\' private data member:

#include 

template

        

Answer 1

I managed to get the following work

#include 

template
class MyVar;

template
void printVar(const MyVar& var);

template
void scanVar(MyVar& var);

template
class MyVar
{
    int x;
    friend void printVar(const MyVar& var);
    friend void scanVar(MyVar& var);
};

template
void printVar(const MyVar& var)
{
    std::cout << var.x << std::endl;
}

template
void scanVar(MyVar& var)
{
    std::cin >> var.x;
}

struct Foo {};

int main(void)
{
    MyVar a;
    scanVar(a);
    printVar(a);
    return 0;
}

UPD: http://en.cppreference.com/w/cpp/language/friend talks about a similar case with operators under "Template friend operators":

A common use case for template friends is declaration of a non-member operator overload that acts on a class template, e.g. operator<<(std::ostream&, const Foo&) for some user-defined Foo

Such operator can be defined in the class body, which has the effect of generating a separate non-template operator<< for each T and makes that non-template operator<< a friend of its Foo

...

or the function template has to be declared as a template before the class body, in which case the friend declaration within Foo can refer to the full specialization of operator<< for its T