Raspberry Pi GPIO polling by wait for event example. Most simple code. No count errors.

gpio_poll.c

/*
  gpio_poll.c
  Raspberry Pi GPIO polling example.
  Hardware: A switch (hardware pulluped) shall be connected to GPIO25.
  Compile: cc gpio_poll.c -o gpio_poll
  Execute: sudo ./gpio_poll.c
*/

#include <fcntl.h>
#include <stdio.h>
#include <poll.h>

int main(){
	int i;
	int fd;
	int ret;
	struct pollfd pfd;
	char c;

	//Enable gpio25
	fd = open("/sys/class/gpio/export", O_WRONLY);
	write(fd, "25", 2);
	close(fd);

	//Set gpio25 as input
	fd = open("/sys/class/gpio/gpio25/direction", O_WRONLY);
	write(fd, "in", 2);
	close(fd);

	//Set gpio25 interrupt
	fd = open("/sys/class/gpio/gpio25/edge", O_WRONLY);
	//write(fd, "falling", 7);
	write(fd, "both", 4);
	close(fd);

	//Wait for event, repeat 10 times
	fd = open("/sys/class/gpio/gpio25/value", O_RDONLY);
	pfd.fd = fd;
	pfd.events = POLLPRI;
	for(i = 1; i <= 10; i++){
		lseek(fd, 0, SEEK_SET);
		ret = poll(&pfd, 1, 3000);
		read(fd, &c, 1);
		printf("%d: ", i);
		if(ret == 0)
			printf("Timeout\n");
		else
			if(c == '0')
				printf("Push\n");
			else
				printf("Release\n", i, c);
	}
	close(fd);

	//Disable gpio25
	fd = open("/sys/class/gpio/unexport", O_WRONLY);
	write(fd, "25", 2);
	close(fd);

	return(0);
}

what does "Release" mean?