c++ - Lambda 返回空字符串

Question

我有学费。

class Fee
{
private:
    std::string _code;
    int _value;
    std::string _description_EN;
    std::string _description_UA;
    std::vector<std::function<std::string()>> get_description;
public:
    //CONSTRUCTORS
    Fee(int value, std::string_view code, std::string_view description_EN, std::string_view description_UA);
    Fee(const std::string _csv_line, const char separator);
    Fee(const Fee &) = delete;
    Fee(Fee &&) = default;
    //OPERATORS
    Fee &operator=(const Fee &) = delete;
    Fee &operator=(Fee &&) = default;
    Fee &operator++() = delete;
    Fee &operator++(int) = delete;
    Fee &operator--() = delete;
    Fee &operator--(int) = delete;
    Fee &operator+(const Fee &other) = delete;
    Fee &operator-(const Fee &other) = delete;
    Fee &operator+=(const Fee &other) = delete;
    Fee &operator-=(const Fee &other) = delete;
    Fee &operator/(const Fee &other) = delete;
    Fee &operator*(const Fee &other) = delete;
    Fee &operator/=(const Fee &other) = delete;
    Fee &operator*=(const Fee &other) = delete;
    Fee &operator%(const Fee &other) = delete;
    Fee &operator%=(const Fee &other) = delete;
    //SETTERS
    void set_new_value(int value);
    //GETTERS
    std::string code();
    int value();
    std::string description(Language language = Language::EN);
    //FUNCTIONS

    //DESTRUCTOR
    ~Fee() = default;
};

和存储费用映射的类 FeeList

class FeeList
{
private:
    std::map<std::string, Fee> _fee_list;
    FeeList() = default;
public:
    static FeeList &fee_list();
    //CONSTRUCTORS
    FeeList(const FeeList &) = delete;
    FeeList(FeeList &&) = delete;
    //OPERATORS
    FeeList &operator=(const FeeList &) = delete;
    FeeList &operator=(FeeList &&) = delete;
    //SETTERS

    //GETTERS
    Fee &fee(const std::string &code);
    //FUNCTIONS
    void addFee(Fee &fee);
    void from_csv_file(const std::string &inv_file, const std::string &um_file, const std::string &id_file, const std::string &tr_file, const char separator);
    //DESTRUCTOR
    ~FeeList() = default;

};

类 Fee 的构造函数具有以下代码行，这些代码行通过 lambdas 填充“get_description” vector

get_description.resize(2);
    get_description[static_cast<size_t>(fee::Language::EN)] = [this]()->std::string{return _description_EN;};
    get_description[static_cast<size_t>(fee::Language::UA)] = [this]()->std::string{return _description_UA;};

这些 lambda 由函数“description(fee::Language::)”调用，它应该返回描述不合适的语言。 实现非常简单

std::string fee::Fee::description(Language language)
{
    return get_description[static_cast<size_t>(language)]();
}

问题是 lambda 返回了空字符串。 我创建了简单的类来测试这种方法并且它按预期工作。我不知道是什么问题。我正在获取其他变量的值(代码和值)，以便正确存储对象。

编辑:这里是 coliru.stacked-crooked.com 的链接，其中粘贴了我的代码并解决了提到的问题(整数值；和字符串代码；是好的字符串描述；是空的)http://coliru.stacked-crooked.com/a/bc56eb53400bd1af 也可以使用 Coliru 命令行找到此文件:cat/Archive2/bc/56eb53400bd1af/main.cpp

Answer 1

隐式实例化的 Fee 移动构造函数复制了 get_description 中的 lambda - 但它没有到达那些 lambda 内部并更新它们捕获的指针。它们仍然指向原始的 Fee 对象，该对象已被移走。然后，您的程序会通过访问移出的对象来表现出未指定的行为。

与其拥有两个单独的字符串变量和一个 lambda vector ，不如拥有一个字符串 vector ？