How to set key repeat rate and delay (in milliseconds) on Windows 10

set_key_repeat_delay.cc

#include <windows.h>
#include <stdlib.h>
#include <stdio.h>

BOOL parseDword(const char* in, DWORD* out)
{
  char* end;
  long result = strtol(in, &end, 10);
  BOOL success = (errno == 0 && end != in);
  if (success)
	{
      *out = result;
	}
  return success;
}

int main(int argc, char* argv[])
{
  FILTERKEYS keys { sizeof(FILTERKEYS) };

  if (argc == 3
      && parseDword(argv[1], &keys.iDelayMSec)
      && parseDword(argv[2], &keys.iRepeatMSec))
	{
      printf("Setting keyrate: delay: %d, rate: %d\n", (int)keys.iDelayMSec, (int)keys.iRepeatMSec);
      keys.dwFlags = FKF_FILTERKEYSON | FKF_AVAILABLE;
	}
  else if (argc == 1)
	{
      puts("No parameters given, so displaying the current value of the key rate delay and speed settings:");
      if (!SystemParametersInfo(SPI_GETFILTERKEYS, sizeof(FILTERKEYS), (LPVOID)&keys, 0)) {
        fprintf(stderr, "System call ``SystemParametersInfo(SPI_GETFILTERKEYS, …)'' failed.");
        return 2;
      }
      printf("delay: %d, rate: %d\n", static_cast<int>(keys.iDelayMSec), static_cast<int>(keys.iRepeatMSec));
      puts("Usage: keyrate <delay ms> <repeat ms>\nCall with no parameters to show the current setting.");
      return 0;
	}
  else
	{
      puts("Usage: keyrate <delay ms> <repeat ms>\nCall with no parameters to show the current setting.\n\nN.B.: I recommend the settings delay=200 and repeat=6");
      return 0;
	}

  if (!SystemParametersInfo(SPI_SETFILTERKEYS, sizeof(FILTERKEYS), (LPVOID)&keys, 0))
	{
      fprintf(stderr, "System call failed.\nUnable to set keyrate.");
	}
  printf("delay: %d, rate: %d\n", (int)keys.iDelayMSec, (int)keys.iRepeatMSec);

  return 0;
}