Variable types with * prefix

Projects Programming
75

the OP may find how this code uses function ptrs and ptrs to arguments to those function insightful. The code manages buttons that perform different "commands". Those cmds are described in a table

int LhTopLimit;

const byte PinLeds [] = { 13, 12, 11 };
const int  NLed       = sizeof(PinLeds);

// -----------------------------------------------------------------------------
void incVar (
    int     val,
    void   *adr )
{
    Serial.print   ("    ");
    Serial.println (*(int *)adr += val);        // cast void* to int*
}

// ---------------------------------------------------------
void setVar (
    int     val,
    void   *adr )
{
    Serial.print   ("    ");
    Serial.println (*(int *)adr  = val);        // cast void* to int*
}

// ---------------------------------------------------------
void toggle (
    int     pin,
    void   *_unused_ )
{
    digitalWrite (pin, ! digitalRead (pin));
}

// ---------------------------------------------------------
struct ButCmd {
    const byte Pin;
    void (*func) (int, void*);      // pointer to function
    int         arg1;
    void       *arg2;               // undefined type
    const char *desc;

    byte            butState;
    unsigned long   msec;
}

cmds [] = {
    { A1, toggle, 13, (void*) 0,           "LED-13" },
    { A2, setVar,  1, (void*) & LhTopLimit, "LhTopLimit" },
    { A3, incVar, -1, (void*) & LhTopLimit, "LhTopLimit--" },
};
const int Ncmd = sizeof (cmds)/sizeof(ButCmd);

// -----------------------------------------------------------------------------

void setup ()
{
    Serial.begin (9600);

    for (int i = 0; i < NLed; i++)
        pinMode (PinLeds [i], OUTPUT);

    for (int i = 0; i < Ncmd; i++) {
        pinMode (cmds [i].Pin, INPUT_PULLUP);
        cmds [i].butState = digitalRead (cmds [i].Pin);
    }
}

// -----------------------------------------------------------------------------
const unsigned long MsecTmout = 500;

void loop ()
{
    unsigned long msec = millis ();

    for (int i = 0; i < Ncmd; i++) {
        if (msec - cmds [i].msec < MsecTmout)
            continue;

        byte but = digitalRead (cmds [i].Pin);
        if (cmds [i].butState != but)
            cmds [i].butState  = but;

        if (LOW == but)  {
            cmds [i].msec      = msec;
            Serial.println (cmds [i].desc);
            (*cmds [i].func) (cmds [i].arg1,cmds [i].arg2);
        }

        cmds [i].msec      = msec;
    }
}