#include <stdio.h>  
#include <stdlib.h>  
#include <fcntl.h>  
#define DEVICE_NAME "/dev/hello"  
int main(int argc, char** argv)  
{  
    int fd = -1;  
    int val = 0;  
    fd = open(DEVICE_NAME, O_RDWR);  
    if(fd == -1) {  
        printf("Failed to open device %s.\n", DEVICE_NAME);  
        return -1;  
    }  
      
    printf("Read original value:\n");  
    read(fd, &val, sizeof(val));  
    printf("%d.\n\n", val);  
    val = 5;  
    printf("Write value %d to %s.\n\n", val, DEVICE_NAME);  
        write(fd, &val, sizeof(val));  
      
    printf("Read the value again:\n");  
        read(fd, &val, sizeof(val));  
        printf("%d.\n\n", val);  
    close(fd);  
    return 0;  
}