A Pure Data external using the Wiring Pi library to listen for button presses on GPIO pin 17

buttonListener.c

#include "m_pd.h"
#include <wiringPi.h>

t_class *buttonlistener_class;

typedef struct _buttonlistener
{
	t_object x_obj;
	t_clock *x_clock;
	int defaultButtonState; //some buttons close switch when pressed, others open it, might as well make the code neutral.
	int buttonState;
	int pinNum;
} t_buttonlistener;

void buttonlistener_tick(t_buttonlistener *x)
{
	int prevState = x->buttonState;
	x->buttonState = digitalRead(x->pinNum);
	if(prevState != x->buttonState){
		if(x->buttonState != x->defaultButtonState){ //bang if button has just been pressed
			outlet_bang(x->x_obj.ob_outlet);
		}
	}
	clock_delay(x->x_clock, 1); //polling every millisecond
}

void *buttonlistener_new()
{
	t_buttonlistener *x = (t_buttonlistener *)pd_new(buttonlistener_class);
	x->x_clock = clock_new(x, (t_method)buttonlistener_tick);
	outlet_new(&x->x_obj, gensym("bang"));
	//call the tick function once to start it
	x->pinNum = 0; //0 is GPIO 17 in wiringPi
	pinMode(x->pinNum, INPUT);
	x->buttonState = digitalRead(x->pinNum);
	x->defaultButtonState = x->buttonState;
	buttonlistener_tick(x);
	return (x);
}

void buttonlistener_free(t_buttonlistener *x)
{
	clock_free(x->x_clock);
}

void buttonlistener_setup()
{
	wiringPiSetup();
	buttonlistener_class = class_new(gensym("buttonlistener"),(t_newmethod)buttonlistener_new,
		(t_method)buttonlistener_free, sizeof(t_buttonlistener), CLASS_NOINLET, 0);
}