I want to make a C++ enum of QString formats to display a QTime

I've been working with C++ on a Time class in Qt and I need to write an enum class that contains the formats that I use in showTime(). Because of the nature of the QString formats I've been getting the following error, the value is not convertible to 'int'. I would gladly appreciate any help or suggestions.

P.S: Here's the code:

enum class TimeFormat {
    a = "hh:mm:ss",
    b = "hh:mm",
    c = "H:m:s a"
};

class Time {
public:
    Time();
    ~Time();

    void setTime(QTime t);
    QString showTime(){
         return time->toString(format);
    }
private:
    QTime* time;
    TimeFormat format;
};

I used a switch statement

enum class TimeFormat {
    format1,
    format2,
    format3,
};

class Time {
public:
    Time();
    ~Time();

    void setTime(int h, int m, int s);
    QString showTime() const{
        QString f;
        switch (format) {
            case TimeFormat::format1:
            f="hh:mm:ss";
            break;
         case TimeFormat::format2:
            f = "hh:mm";
            break;
         case TimeFormat::format3:
            f= "H:m:s a";
            break;
         }
         return time->toString(f);
    }

    void changeFormat(TimeFormat f);
private:
    QTime* time;
    TimeFormat format;
};