不存在从到 * 的合适转换存在

Question

I am using linked lists to manipulate a sorted list. However, in my function PutUser, I am getting an error when calling on another function to compare two users. I am not sure what to do or how to handle the error.

Here is my NodeUser struct (creates nodes for the linked list):

struct NodeUser { 
    User user;
    NodeUser* nextOnList;
};

I then have a function that is suppose to create a new node and put a user into the list

void SortedList::PutUser(User* user) {
    NodeUser* newNode; /
    NodeUser* previousPointer; 
    NodeUser* location; 
    bool moreToSearch;

    location = topOfList;
    previousPointer = NULL;
    moreToSearch = (location != NULL);

    while (moreToSearch) {
        switch (user->comparedTo(location->user)) {
        case GREATER:
            previousPointer = location;
            location = location->next;
            moreToSearch = (location != NULL);
            break;
        case LESS:
            moreToSearch = false;
            break;
        }
    }
    newNode = new NodeUser;
    newNode->user = user;

    if (previousPointer == NULL) {
        newNode->next = topOfList;
        topOfList = newNode;
    }
    else {
        newNode->next = location;
        previousPointer->next = newNode;
    }
    length++;
}

I am getting the error at (specifically location is underlined in red (error)):

switch (user->comparedTo(location->user))

How to fix the error at the switch?

Answer 1

You are trying to pass a User object where a User* pointer is expected.

There is no reason to pass a User object by pointer into SortedUserType::PutUser() or User::comparedTo() . Pass it in by reference instead:

class User {
public:
    ...
    RelationType comparedTo(const User &aUser) const;
    ...
};

void SortedUserType::PutUser(const User &user) {
    ...
    while (moreToSearch) {
        switch (user.comparedTo(location->user)) {
        ...
    }
    ...
    newNode = new NodeUser;
    newNode->user = user;
    ...
}

Answer 2

A quick fix would be to

RelationType comparedTo(User const &aUser) const;

Or at least

switch (user->comparedTo(&location->user))

Pointers should not be overused.