How would I code an array of PHYSICAL_MONITOR in Delphi?

I am trying to make Delphi talk to the WinAPI function GetPhysicalMonitorsFromHMONITOR().

How would I setup the needed data structure?

Currently, I have:

  LPPHYSICAL_MONITOR = record
    hPhysicalMonitor: THandle;
    szPhysicalMonitorDescription: array [0..127] of WideChar;
  end;
  PLPPHYSICAL_MONITOR = ^LPPHYSICAL_MONITOR;

However, the function expects an array – and I need an array, when I dereference the Pointer structure in order to get first, second ... monitor.

This is what I have for the function itself:

function GetPhysicalMonitorsFromHMONITOR(hMonitor: HMONITOR;
   dwPhysicalMonitorArraySize: DWORD;
   pPhysicalMonitorArray: PLPPHYSICAL_MONITOR): Boolean;
   stdcall; external 'Dxva2.dll' Name 'GetPhysicalMonitorsFromHMONITOR';

Solution

Per the same documentation you linked to:

To get the required size of the array, call GetNumberOfPhysicalMonitorsFromHMONITOR.

So, get the array size first, then allocate the array, then pass the array to GetPhysicalMonitorsFromHMONITOR(). The same documentation you linked to even provides an example of that (in C, which can easily be translated to Delphi).

Try something like this:

const
  PHYSICAL_MONITOR_DESCRIPTION_SIZE = 128;

type
  PHYSICAL_MONITOR = record
    hPhysicalMonitor: THandle;
    szPhysicalMonitorDescription: array[0..PHYSICAL_MONITOR_DESCRIPTION_SIZE-1] of WideChar;
  end;
  LPPHYSICAL_MONITOR = ^PHYSICAL_MONITOR;

function GetNumberOfPhysicalMonitorsFromHMONITOR(hMonitor: HMONITOR;
  pdwNumberOfPhysicalMonitors: LPDWORD): BOOL;
  stdcall; external 'Dxva2.dll' name 'GetNumberOfPhysicalMonitorsFromHMONITOR';

function GetPhysicalMonitorsFromHMONITOR(hMonitor: HMONITOR;
  dwPhysicalMonitorArraySize: DWORD;
  pPhysicalMonitorArray: LPPHYSICAL_MONITOR): BOOL;
  stdcall; external 'Dxva2.dll' name 'GetPhysicalMonitorsFromHMONITOR';

function DestroyPhysicalMonitors(dwPhysicalMonitorArraySize: DWORD;
  LPPHYSICAL_MONITOR pPhysicalMonitorArray): _BOOL;
  stdcall; external 'Dxva2.dll' name 'DestroyPhysicalMonitors';

var
  hMonitor: HMONITOR;
  cPhysicalMonitors, I: DWORD;
  pPhysicalMonitors: array of PHYSICAL_MONITOR;
begin
  // Get the monitor handle.
  hMonitor = ...;

  // Get the number of physical monitors.
  if not GetNumberOfPhysicalMonitorsFromHMONITOR(hMonitor, @cPhysicalMonitors) then
    RaiseLastOSError;

  if cPhysicalMonitors = 0 then
    Exit;

  // Allocate the array of PHYSICAL_MONITOR structures.
  SetLength(pPhysicalMonitors, cPhysicalMonitors);

  // Get the array.
  if not GetPhysicalMonitorsFromHMONITOR(hMonitor, cPhysicalMonitors, @pPhysicalMonitors[0]) then
    RaiseLastOSError;
  try
    for I := 0 to cPhysicalMonitors-1 do
    begin
      // Use pPhysicalMonitors[I] as needed.
    end;
  finally
    // Close the monitor handles.
    DestroyPhysicalMonitors(cPhysicalMonitors, @pPhysicalMonitors[0]);
  end;
end;