Is there a way to detect if a monitor is plugged in?

Question

I have a custom application written in C++ that controls the resolution and other settings on a monitor connected to an embedded system. Sometimes the system is booted headless and run via VNC, but can have a monitor plugged in later (post boot). If that happens he monitor is fed no video until the monitor is enabled. I have found calling "displayswitch /clone" brings the monitor up, but I need to know when the monitor is connected. I have a timer that runs every 5 seconds and looks for the monitor, but I need some API call that can tell me if the monitor is connected.

Here is a bit of psudocode to describe what I'm after (what is executed when the timer expires every 5 seconds).

if(If monitor connected) 
{
   ShellExecute("displayswitch.exe /clone);
}else
{
   //Do Nothing
}

I have tried GetSystemMetrics(SM_CMONITORS) to return the number of monitors, but it returns 1 if the monitor is connected or not. Any other ideas?

Thanks!

Answer 1

Try the following code

BOOL IsDisplayConnected(int displayIndex = 0)
{
    DISPLAY_DEVICE device;
    device.cb = sizeof(DISPLAY_DEVICE);
    return EnumDisplayDevices(NULL, displayIndex, &device, 0);
}

This will return true if Windows identifies a display device with index (AKA identity) 0 (this is what the display control panel uses internally). Otherwise, it will return false false. So by checking the first possible index (which I marked as the default argument), you can find out whether any display device is connected (or at least identified by Windows, which is essentially what you're looking for).