C++ template member function not declared in this scope

Question

I'm trying to create a linked list, but when I run IsEmpty(test) it just says it was not declared in this scope even though it's public.

I'm pretty new at templates, but I couldn't find the answer on google so I have to ask here. Anyone know what the problem is?

Also, the error points to main() where I call IsEmpty()

//.h
template <typename ItemType>
class Node
{
    public:
        ItemType Data;
        Node <ItemType> *next;
        int position;
};

template <typename ItemType>
class Linked_List
{
        public:
        Node <ItemType> *start;
        Linked_List();
        bool IsEmpty();
}


//.cpp  
#include "Linked_List.h"
#include <iostream>
#include <cstdlib>
using namespace std;

template <typename ItemType>
Linked_List <ItemType>::Linked_List(){
    start = NULL;
}

template <typename ItemType>
bool Linked_List <ItemType>::IsEmpty(){
    if (start == NULL){
        return true;
    }
    return false;
}

int main(){
    Linked_List <int> test;
    cout << IsEmpty(test) << endl;   //error points to here
}

score 2 · Accepted Answer · answered May 08 '14 at 15:14

2

The correct way to invoke a member function is obj.function(...). You need:

cout << test.IsEmpty() << endl;   //error points to here

answered May 08 '14 at 15:14

R Sahu

204,454
14
159
270

Ahh thanks a lot, I feel dumb – Seb May 08 '14 at 15:17
@Foxic You are welcome. We all do dumb things once in a while :) – R Sahu May 08 '14 at 15:23

score 1 · Answer 2 · answered May 08 '14 at 15:15

1

Templates have to be declared and defined in header files.

answered May 08 '14 at 15:15

kaman

376
1
8

I see, it seems to be working fine though. Any reason why? Edit:nvm just saw that link posted – Seb May 08 '14 at 15:18
http://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file this should answer your question – kaman May 08 '14 at 15:21

score 0 · Answer 3 · answered May 08 '14 at 15:25

Template headers do not work as non-template headers. You must define your template functions inside the header. Just move the definitions you have on the .CPP file to the end of your .h file.

After you have done that you can invoke the function from the object you have created.

C++ template member function not declared in this scope

3 Answers3