Read and Write to a Keyboard device in Linux using C++

I had to write some userspace code to read and write to a keyboard device in Linux using C++.  I thought it would be as simple and open(), read() and write().  I was close but was missing a couple key items: scan codes and input_event.

Open Device
Opening the keyboard device is the same as opening any other device in linux

int fd =0;
char *device = "/dev/input/event1";
if( (fd= open(device, O_RDWR))< 0 )
{
     // Read or Write to device
}

Read Keyboard Device
Read from the keyboard device.  Instead of passing a char array as the buffer, pass an input_event struct to store the results of the read.  KEY_UP or any other scan code numeric value is specific to your Linux key mapping.  KEY_UP is defined for your Linux setup so do not forget to include linux/input.h.  Use the definition for the key scan code and not the actual scan code numeric value.

#include <linux/input.h>
#define EV_PRESSED 1
#define EV_RELEASED 0
#define EV_REPEAT 2

struct input_event event;
unsigned int scan_code = 0;
int num_bytes = read(fd,&event, sizeof(struct input_event));
if(event.type!= EV_KEY)
     return;  // Keyboard events are always of type EV_KEY

if(event.value== EV_RELEASED)
{
     scan_code = event.code;
     if(scan_code == KEY_UP)
          // Do something if keyboard up arrow pressed
}

Write to Keyboard Device
To write to the device, you populate the input_event struct with the key scan code.  You also set the type to EV_KEY and the value to either “press” or “release”.  To represent a keyboard, you must do a press and a release because some code may be looking for a key press or a key released.

struct input_event event;
// Press the key down
event.type = EV_KEY;
event.value = EV_PRESSED;
event.code = KEY_UP;
write(fd, &event, sizeof(struct input_event));

// Release the key
event.value = EV_RELEASED;
event.code = KEY_UP;
write(fd, &event, sizeof(struct input_event));