SDL_DisplayMode* SDL_GetClosestDisplayMode(int                    displayIndex,
                                           const SDL_DisplayMode* mode,
                                           SDL_DisplayMode*       closest)

// Using SDL2's SDL_GetClosestDisplayMode()
#include <SDL2/SDL.h>
#include <cstdio>

int main(int argc, char* argv[]){

  SDL_Init(SDL_INIT_VIDEO);

  // Declare structures to be filled in.
  SDL_DisplayMode target, closest;

  // Set the desired resolution, etc.
  target.w = 600;
  target.h = 500;
  target.format = 0;  // don't care
  target.refresh_rate = 0; // don't care
  target.driverdata   = 0; // initialize to 0
  printf("Requesting: \t%dx%dpx @ %dhz \n", target.w, target.h, target.refresh_rate);

  // Pass the display mode structures by reference to SDL_GetClosestDisplay
  // and check whether the result is a null pointer.
  if(SDL_GetClosestDisplayMode(0, &target, &closest)==NULL)

    // If the returned pointer is null, no match was found.
    printf("\nNo suitable display mode was found!\n\n");

  else
    // Otherwise, a display mode close to the target is available.
    // Access the SDL_DisplayMode structure to see what was received.
    printf("  Received: \t%dx%dpx @ %dhz \n", closest.w, closest.h, closest.refresh_rate);

  // Clean up and exit the program.
  SDL_Quit();
  return 0;

}