Question

I am compiling my code with g++ -g and I am getting the error message in the title.

The error is related to a function I have made, it’s signature being:

void addHead( Elem *&start , Elem *newStart );

and I am passing this function these two variables:

Elem * head;    
Elem * tempEl;

so that it looks like this:

addHead( *head , *tempEl );

The actual function is:

void addHead( Elem start , Elem newStart )
{
Elem listItem;

listItem = newStart;
*listItem.next = start;
start = listItem;
}

It pre-pends the second argument to the the beginning of a linked-list starting at the first argument.

I have been pulling my hair out with this one. No matter what I do I keep getting this error!

cannot convert Elem to Elem* for argument 1 to void addHead(Elem*, Elem*)

Edit: Forgot this error is in there too:

error: invalid initialization of reference of type Elem*& from expression of type Elem

Answer 1

It’s being pretty specific: You’re passing an Elem, but it takes an Elem*. In particular, head is of type Elem*, but you are passing *head: of type Elem.

Also, your definition signature doesn’t match your definition, so even when you fix the call, you will get a linker error when it can’t find addHead(Elem*, Elem*). Definitions must exactly their signatures (more correctly, declarations). Of course, neither of these changes will fix the actual implementation of addHead(), but that’s your homework 🙂