request_refresh_rate - Requests a specific refresh rate during graphic mode switch. Allegro game

       Requests that the next call to set_gfx_mode() try to use the specified refresh rate, if possible. Not all
       drivers are able to control this at all, and even when they can, not all rates will be  possible  on  all
       hardware,  so the actual settings may differ from what you requested.  After you call set_gfx_mode(), you
       can use get_refresh_rate() to find out what was actually selected. At the moment only the DOS VESA 3.0, X
       DGA 2.0 and some Windows DirectX drivers support this function. The speed is specified in Hz, eg. 60, 70.
       To return to the normal default selection, pass a rate value of zero. Example:

          request_refresh_rate(60);
          if (set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0) != 0)
             abort_on_error("Couldn't set graphic mode!");
          if (get_refresh_rate() != 60)
             abort_on_error("Couldn't set refresh rate to 60Hz!");

       request_refresh_rate  -  Requests  a  specific  refresh  rate  during  graphic  mode switch. Allegro game
       programming library.

set_gfx_mode(3alleg4), get_refresh_rate(3alleg4)

Allegro                                           version 4.4.3                    request_refresh_rate(3alleg4)

#include<allegro.h>voidrequest_refresh_rate(intrate);