Question

I have a rather simple question that I could normally debug myself, but I seem to be having quite the problem at this point in time.

I am creating a linked list data structure and I made two functions, one to return the front Elem and one to return the last Elem. The issue is that the compiler is saying that Elem does not define a type, when it does.

Here is the header file trimmed down the the relevant code:

class simpleList {

    public:
        //Returns a pointer to the first Elem of the list
        simpleList::Elem* front();

        //Returns a pointer to the last Elem of the list
        simpleList::Elem* back();

    private:
        struct Elem {
            char info;
            Elem *next;
        };

        Elem *head; 
};

and here is the .cpp file implementation of these two functions:

//Returns a pointer to the first Elem of the list
simpleList::Elem* simpleList::front()
{
    return head;
}

//Returns a pointer to the last Elem of the list
simpleList::Elem* simpleList::back()
{
    Elem * temp = head;

    while( temp -> next != 0 )
        temp = temp -> next;

    return temp;
}

I have tried both scoping them to the class and just doing:

Elem* simpleList::front()
Elem* simpleList::back()

The error message is as follows:
simpleList.h:38:9: error: ‘Elem’ in ‘class simpleList’ does not name a type
simpleList.h:41:9: error: ‘Elem’ in ‘class simpleList’ does not name a type

Answer 1

Try this order for the class declaration:

class simpleList {
    public:

        struct Elem {
            char info;
            Elem *next;
        };

        //Returns a pointer to the first Elem of the list
        Elem* front();

        //Returns a pointer to the last Elem of the list
        Elem* back();

    private:
        Elem *head; 

};