C ++-访问静态void函数上的变量

Question

This is my callback-function (ALOG is for debugging)

static void playerEventCallbackA(void *clientData, SuperpoweredAdvancedAudioPlayerEvent event, void *value) {
    ALOG("###################### CALLBACK PLAYER A.... ");
    if (event == SuperpoweredAdvancedAudioPlayerEvent_LoadSuccess) {
        ALOG("###################### CALLBACK PLAYER A.... loaded"); 
        SuperpoweredAdvancedAudioPlayer *playerA = *((SuperpoweredAdvancedAudioPlayer **)clientData);        
        playerA->setBpm(126.0f);
        playerA->setFirstBeatMs(353);
        playerA->setPosition(playerA->firstBeatMs, false, false);
    };
}

i need to set the bpm here, which i have detected on a other function in this class. How can I manage this?

Answer 1

You cannot, since static function has no this parameter. You can access only static members, or send object of needed type to static function.

Answer 2

You have either to pass an object of the class to the function and use within the function the data members of the object or to create an object of the class as a local variable of the function and access the data members of the object.

For example

#include <iostream>

class A
{
private:
    float a, b, c;
public:
    A( float a, float b, float c ) : a( a ), b( b ), c( c )
    {
    }

    static void display_average( const A &a )
    {
        std::cout << ( a.a + a.b + a.c ) / 3 << std::endl;
    }
};

int main()
{
   A a( 10.10f, 20.20f, 30.30f );

   A::display_average( a );
}