Get screen resolutions using low-level CoreGraphics primitives

screen-size.c

#include <stdio.h>
#include <CoreGraphics/CoreGraphics.h>

// clang -framework CoreGraphics -o screen-size-cg -arch x86_64 -arch arm64 screen-size.c


static void ShowDisplay(CGDirectDisplayID id)
{
    CGRect frame = CGDisplayBounds(id);
    CGSize resolution = frame.size;
    printf("%ldx%ld\n", (long) resolution.width, (long) resolution.height);
}

static void ShowAllDisplays(void)
{
    uint32_t maxDisplays = 16;   /* There can't be more than 16 displays, right? */
    uint32_t actualDisplays = 0;
    CGDirectDisplayID displayIDs[maxDisplays];
    int error = CGGetActiveDisplayList(maxDisplays, displayIDs, &actualDisplays);

    if (error != kCGErrorSuccess) {
        fprintf(stderr, "Error: %d\n", error);
        return;
    }

    for (int i = 0; i < actualDisplays; i++) {
        printf("%2d ", i);
        ShowDisplay(displayIDs[i]);
    }
}


static void ShowMainDisplay(void)
{
    ShowDisplay(CGMainDisplayID());
}


int main(int argc, char **argv)
{
    int ec = 0;

    ShowMainDisplay();
    printf("\n");
    ShowAllDisplays();

quit:
    return ec;
}