(C++) 从另一个类访问变量时的值无效

Question

Whenever I try to access time_series_length from the Example class I get an invalid number.

class Indicator
{
public:
    Indicator(){};
    Indicator(std::vector<DayData> data, int days)  // days = 30 from the main function
    {
        time_series = data;
        time_series_length = days;
        std::cout << time_series_length << std::endl; // PRINTS OUT (30) in the console
    };

    // Returns the length in days of the time series
    int get_ts_length()
    {
        return time_series_length;
    }

    // Returns the time series in a vector of DatData structs
protected:
    int time_series_length;  // the length of the time_series in days
    std::vector<DayData> time_series;
};

class Example : public Indicator
{
public:
    Example(){};
    void check()
    {
        std::cout << Indicator::time_series_length;  // PRINTS OUT (-349926832) in the console
    }
};

struct DayData
{
    double adj_close;
    int volume;
};

int main()
{
    const int days = 30;

    // ... I populate data with DayData structs

    Indicator(data, days);

    Example a;
    a.check();
    return 0;
}

I should get output

30
30

,instead I get

30
-349926832

Answer 1

You did not assign anyting to the created instance of the Example object a . It was only initialized. It dedicated a piece of memory to your class, but did not put anything in there, it's a random value in memory.

Answer 2

Initialization is missing for the Indicator class, which is part of "Example a;" You have to call Indicator initialization with object -> a; so you call respective method -> get_ts_length() instead data member as good coding practice.