C++ Array function pointer with class

Question

Below is my class code :

enum style{BASIC, WEATHER_ONLY};
enum area{AREA0, AREA1, AREA2, AREA3, AREA4, AREA5, NULL_AREA};
enum display{NTP_TIME, TWO_DAY_WEATHER, TREE_DAY_WEATHER, WEEK_WEATHER, TEMPERATURE_AND_HUMIDITY};

typedef struct areaFormat
{
    unsigned int x0;
    unsigned int y0;
    unsigned int width;
    unsigned int height;
    unsigned int nextSpace;
}AreaFormat;

class DisplayTemplate
{
    public:
        void NTPTime(AreaFormat range);
        void TwoDayWeather(AreaFormat range);
        void TreeDayWeather(AreaFormat range);
        void WeekWeather(AreaFormat range);
        void TemperatureAndHumidity(AreaFormat range);
        
        typedef struct setting
        {
            AreaFormat areaParameter;
            void (DisplayTemplate::*function)(AreaFormat);
        }BlockParameter;

        void (DisplayTemplate::*Display[7])(AreaFormat) = {&DisplayTemplate::NTPTime, &DisplayTemplate::TwoDayWeather, &DisplayTemplate::TreeDayWeather, &DisplayTemplate::WeekWeather, &DisplayTemplate::TemperatureAndHumidity};

        BlockParameter displayStyle[TEMPLATE_MAX_STYLE][DISPLAY_MAX_BLOCK] =
        {
            {
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=AREA2}, .function=Display[NTP_TIME]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[TWO_DAY_WEATHER]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=AREA3}, .function=Display[TREE_DAY_WEATHER]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[WEEK_WEATHER]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[TEMPERATURE_AND_HUMIDITY]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[NTP_TIME]}
            },
            {
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=AREA2}, .function=Display[NTP_TIME]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[TWO_DAY_WEATHER]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=AREA3}, .function=Display[TREE_DAY_WEATHER]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[WEEK_WEATHER]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[TEMPERATURE_AND_HUMIDITY]},
                {.areaParameter ={.x0=0, .y0=0, .width=0, .height=0, .nextSpace=NULL_AREA}, .function=Display[NTP_TIME]}
            }
        };
};

My main.cpp :

DisplayTemplate dt;
AreaFormat af;

dt.displayStyle[BASIC][AREA0].function(af);

But compile show error as below : error: must use '.' or '->' to call pointer-to-member function in '((DisplayTemplate*)this)->DisplayTemplate::Display[0] (...)', e.g. '(... ->* ((DisplayTemplate*)this)->DisplayTemplate::Display[0]) (...)

In array displayStyle function is equal DisplayTemplate::Display function, but why i can't call function?

Answer 1

Syntax to call a member function when you have a pointer to member function is:

(obj.*memberFuncPtr)(args);

so you should:

DisplayTemplate dt;
auto ptr = dt.displayStyle[BASIC][AREA0].function;
auto af = dt.displayStyle[BASIC][AREA0].areaParameter;
(dt.*ptr)(af);

---

If auto is not clear, you can add alias type for member function pointer

using FuncMemPtr = void (DisplayTemplate::*)(AreaFormat);

to DisplayTemplate, then:

DisplayTemplate::FuncMemPtr ptr = dt.displayStyle[BASIC][AREA1].function;