指针在第二次迭代后不再工作

我在reddits dailyprogrammer做定期的挑战，学习和练习C++。在上周的挑战中，我被一些带有指针的东西卡住了。

挑战在于/曾经创建一个带有类别的待办事项列表。我已经在上一个挑战中实现了待办事项列表部分，我从那里开始工作。

这是我为这个挑战准备的代码：

#include <string>
#include <algorithm> 
#include <iostream> 
#include <vector>
#include <iterator>
class TodoItem;
class Category{
public:
    Category(std::string name)
        : name(name) {
    }
    void addToCategory(TodoItem* item){
        items.push_back(item);
    }
    void removeFromCategory(const TodoItem* item){
        auto it = std::find(items.begin(), items.end(), item);
        if (it != items.end())
        {
            items.erase(it);
        }
    }
    static Category combine(const Category &left, const Category &right){
        Category combined(left.getName() + ", " + right.getName());
        std::vector<TodoItem*> sortedLeft(left.items);
        std::vector<TodoItem*> sortedRight(right.items);
        std::sort(sortedLeft.begin(), sortedLeft.end());
        std::sort(sortedRight.begin(), sortedRight.end());
        std::set_intersection(sortedLeft.begin(), sortedLeft.end(), sortedRight.begin(), sortedRight.end(), std::back_inserter(combined.items));
        return combined;
    }
    std::string getName() const{
        return name;
    }
    bool operator==(const Category& a) const {
        return a.getName() == getName();
    }
    bool operator!=(const Category& a) const {
        return a != *this;
    }
    bool operator<(const Category& a) const {
        return this->getName() < a.getName();
    }
    friend std::ostream& operator<<(std::ostream& os, const Category& category);
private:
    std::string name;
    std::vector<TodoItem*> items;
};
class TodoItem
{
public:
    TodoItem(const std::string &item)
        : task(item) {
    }
    void update(const std::string &item){
        task = item;
    }
    std::string getTask() const{
        return task;
    }
    bool operator==(const TodoItem& a) const {
        return a.getTask() == getTask();
    }
    bool operator!=(const TodoItem& a) const {
        return a != *this;
    }
    bool operator<(const TodoItem& a) const {
        return this->getTask() < a.getTask();
    }
    friend std::ostream& operator<<(std::ostream& os, const TodoItem& item) {
        os << item.getTask() << std::endl;
        return os;
    }
private:
    std::string task;
};

inline std::ostream& operator<<(std::ostream& os, const Category& category) {
    os << "----" << category.getName() << "----" << std::endl;
    for (auto &item : category.items){
        os << *item << std::endl;
    }
    return os;
}
class TodoList
{
public:
    void add(const std::string &task, const std::string &category = "No category"){
        Category* catPtr = nullptr;
        for (size_t j = 0; j < categories.size(); j++)
        {
            if (categories[j] == Category(category))
            {
                catPtr = &categories[j];
                break;
            }
        }
        if (catPtr == nullptr)
        {
            categories.push_back(Category(category));
            catPtr = &categories[categories.size() - 1];
        }

        for (size_t i = 0; i < items.size(); i++)
        {
            if (items[i] == TodoItem(task))
            {
                catPtr->addToCategory(&items[i]);
                return;
            }
        }
        items.emplace_back(TodoItem(task));
        catPtr->addToCategory(&items[items.size() - 1]);
    }
    template<typename ... args>
    void add(const std::string &task, const std::string &category, args... otherCategories){
        add(task, category);
        add(task, otherCategories...);
    }
    void update(const std::string &oldTask, const std::string &newTask){
        auto itemIt = std::find(items.begin(), items.end(), TodoItem(oldTask));
        if (itemIt != items.end())
        {
            itemIt->update(newTask);
        }
    }

    template<typename ... args>
    void viewList(std::ostream& os, args ... categoriesArgs) const{
        os << getCategory(categoriesArgs...);
    }
private:
    Category getCategory(const std::string category) const{
        return *std::find(categories.begin(), categories.end(), Category(category));
    }
    template<typename ... args>
    Category getCategory(const std::string category, args ... categoriesArgs) const{
        return  Category::combine(*std::find(categories.begin(), categories.end(), Category(category)), getCategory(categoriesArgs...));
    }

    std::vector<TodoItem> items;
    std::vector<Category> categories;
};

int main(){
    TodoList list;
    list.add("A pixel is not a pixel is not a pixel", "Programming");
    list.add("The Scheme Programming Language", "Programming");
    list.add("Memory in C", "Programming");
    list.add("Haskell's School of Music", "Programming", "Music");
    list.add("Algorithmic Symphonies from one line of code", "Programming", "Music");
    list.add("Modes in Folk Music", "Music");
    list.add("The use of the Melodic Minor Scale", "Music");
    list.viewList(std::cout, "Music");
    list.viewList(std::cout, "Programming");
    list.update("Algorithmic Symphonies from one line of code", "Algorithmic Symphonies from one line of code in C");
    list.viewList(std::cout, "Programming", "Music");
    return 0;
}

但是当我执行它时，我在方法 TodoList::Add 中出现错误的内存异常。

当我执行这些行时，指向上一个待办事项的指针变为 invallid。

        items.emplace_back(TodoItem(task));
        catPtr->addToCategory(&items[items.size() - 1]);

有人可以向我解释为什么会发生这种情况以及我如何解决这个问题吗？

PS：我正在使用Visual Studio，不要认为这很重要。