c++ - ostream must take exactly one argument -

i getting compile error in output stream operator , cannot seem find out how fix never received error before:

linkedlist.cpp:258: error: ‘std::ostream& linkedlist<t>::operator<<(std::ostream&, linkedlist<t>)’ must take 1 argument make: *** [linkedlist.o] error 1 

here definition of operator<<

template <class t> ostream& linkedlist<t>::operator<<(ostream &output, linkedlist<t> list) {     node *curr;     curr=list.head;      while(curr!=null )     {         output << curr->data;         curr = curr->next;     }      return output; } 

here in header:

//ostream operator printing list template <class t> ostream &operator<<(ostream &output, linkedlist<t> list); 

any appreciated!

you defined member function, have define free standing (probably friend) function, either

1. outside class

   template <class u> ostream& operator<<(ostream &output, linkedlist<u> list){...} 

in case have declare inside class

template <class u> // note different type name  friend ostream& operator<<(ostream &output, linkedlist<u> list) 

or

2. inside class as

   // no need template, type passed automatically function not templated anymore friend ostream& operator<<(ostream &output, linkedlist list){...}  

the difference between these 2 declarations bit subtle, purpose both work equally well. , want pass linkedlist const reference, linkedlist<t>& list.

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edit

a common mistake declare friend operator inside class as

template<typename t> class linkedlist {     //....     friend ostream& operator<<(ostream& output, const linklist& list); // declaration } 

then try define outside class as

template<typename t> ostream& operator<<(ostream& output, const linklist<t>& list){...} 

guess what? code compile, won't link, declaration inside class declares non-template function, 1 each type t pass linklist<t>. then, when declare e.g. linklist<int> lst, , try cout << lst, compiler see declaration of friend, looks like

friend ostream& operator<<(ostream& output, const linklist<int>& list); 

and try searching definition. there no definition in rest of header, template operator, linker isn't able find implementation , spit linker error. live example here.