kindly suggest the mistake in following code?

Question

#include<iostream.h>
template<class T>
class myclass;

template<class T>
void f(myclass<T> &c);

template<class T>
class myclass
{
    private:
        T value;
    public:
        friend void f(myclass<T> &c);

    T getvalue()
    {
        return value;
    }
    void setvalue(T v)
    {
        value=v;
    }
};

template<class T>
void f(myclass<T> &c)
{
    cout<<endl<<"function called:\n";
    cout<<c.getvalue()<<endl;
}
int main()
{
    myclass<int> object;
    object.setvalue(6);
    f(object);
    return 0;
}

This code is regarding templates with friend functions. While running the code, I am getting the following error:

error:undefined reference to f(myclass &) in line 22

kindly suggest. thanks in advance.

c free....i am working with.....it was value=v; but it is solved now..thanks!! — neha, Apr 12 '15 at 11:08

score 0 · Answer 1 · answered Apr 12 '15 at 09:12

0

Declare the friend function like

friend void f<>(myclass<T> &c);

Also in "new" C++ header iostream shall be specified like

#include <iostream>

and you should use directive

using namespace std;

if you do not want to change the other code in the program.

answered Apr 12 '15 at 09:12

Vlad from Moscow

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hey thanks...dis too worked.....but this compiler works with old syntax of header file.....so second suggestion wont work with it – neha Apr 12 '15 at 11:00
@neha It seems your old compiler does not support namespace names.:) – Vlad from Moscow Apr 12 '15 at 11:37

score 0 · Answer 2 · answered Apr 12 '15 at 09:13

0

You missed to specify the template in the friend declaration:

template<typename U>
friend void f(myclass<U> &c);

See a fully working sample here please.

answered Apr 12 '15 at 09:13

πάντα ῥεῖ

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but why is it required to specify different template argument U when we have used T in forward declaration....when we use T it shows error...why so? – neha Apr 12 '15 at 10:57
@neha _"when we use T it shows error...why so? "_ Because `T` is already used by the enclosing template class. – πάντα ῥεῖ Apr 12 '15 at 10:59

kindly suggest the mistake in following code?

2 Answers2