Error in calling a function defined within a struct

Question

I've been provided with a code to create a doubly-linked list. A node in the linked list is a struct by the name of ListItem. Now within that node is a function that assigns a value to the node. The problem that I'm having is that I can't seem to create a node and use the function to assign the value to it.

Here's the code for the struct "ListItem".

template <class T>
struct ListItem
{
    T value;
    ListItem<T> *next;
    ListItem<T> *prev;

    ListItem(T theVal)
    {
        this->value = theVal;
        this->next = NULL;
        this->prev = NULL;
    }
};

The corresponding ListItem functions in the accompanying .cpp file:

template <class T>
ListItem<T>* List<T>::getHead()
{
}

template <class T>
ListItem<T>* List<T>::getTail()
{
}

template <class T>
ListItem<T> *List<T>::searchFor(T item)
{
}

Here's what I was attempting to do in my main function.

int main()
{
    ListItem<int> a;
    a.ListItem(int 5);
    system("PAUSE");
}

All I'm trying to do here is create a node and assign a value to it. Following are the errors I'm getting:

='a' is not a class or namespace

=missing template arguments before '(' token

=expected primary expression before 'int'

Some programmer dude · Accepted Answer · 2013-02-07 07:23:34Z

3

Remember that a struct is just the same as a class, so what you've done is create a class with the name ListItem containing a normal constructor taking a single argument.

You create it like normal:

ListItem<int> a(5);

You have some other problems as well, like having functions for the class that are not declared in the class (e.g. the getHead function). You also can not have the implementation of templated function members in a separate source file, they have to be in the header file together with the class (or struct) definition.

answered Feb 7, 2013 at 7:23

Some programmer dude

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2 Comments

mrsinister Over a year ago

Thanks a lot for the response, first of all. I get your point about the functions not being declared in the class/struct, but I don't get your point about member functions being declared in a separate file. Take getHead, for example. Are you saying the implementation of getHead should be within the class definition?

Some programmer dude Over a year ago

@SaadTariq When a templated class is used, it need the complete definition, not only the class but the functions too. Either place the functions inline in the class, or place them separately after the class definition (like you have now, but put the functions in the header file instead of a separate source file).

Marius Bancila · Accepted Answer · 2013-02-07 07:24:54Z

2

ListItem is not a function name, but the constructor of the class/structure. The constructor is a special function and cannot be called like that. Your code should look like this:

int main()
{
    ListItem<int> a(5);
    system("PAUSE");
}

answered Feb 7, 2013 at 7:24

Marius Bancila

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