I’m trying to code 2-3 tree with string keys but compare method doesn’t work in searchNode().
I don’t understand why I can’t compare key with class field. Maybe there is another way to compare std::string variables. Help me please

#include <iostream>
#include <string>

class TwoThreeTree
{
public:
    TwoThreeTree() : root_(nullptr) {}
    bool searchKey(const std::string& key) const;
private:
    struct Node 
    {
        std::string key1_, key2_;
        Node* left_;
        Node* middle_;
        Node* right_;
        Node(std::string key1, std::string key2 = nullptr, 
            Node* left = nullptr, Node* middle = nullptr, Node* right = nullptr) :
            key1_(key1),
            key2_(key2),
            left_(left),
            middle_(middle),
            right_(right)
        { }
    };
    Node* root_{ nullptr };
    Node* searchNode(const std::string& key) const
    {
        if (root_ == nullptr)
        {
            return false;
        }

        Node* current = root_;

        int c = key.compare(" ");

        while (current != nullptr && (current->key1_ != key || current->key2_ != key))
        {
            if (current->left_.compare(key) < 0 && key.compare(current->right_) < 0)
            {
                current = current->middle_;
            }
            else if (key.compare((current->right_)) > 0)
            {

            }
        }
    }
};