Print the monitor's name with EnumDisplayDevices in Delphi - delphi

Question

I need to read some information regarding the monitors connected through the EnumDisplayDevicesA function.
I tried to convert the following example written in c++ to delphi, but I have a problem when I try to read the device name from the PDISPLAY_DEVICEA structure LDeviceName := LDisplayDevice.deviceName; as it only returns Chinese characters.
I think it is a problem related to character encoding but I don't know how to fix it.
My source code:
program Monitor;
{$APPTYPE CONSOLE}
uses
System.SysUtils;
const
user32 = 'user32.dll';
type
LONG = LongInt;
BOOL = LongBool;
PDISPLAY_DEVICE = ^DISPLAY_DEVICE;
LPCSTR = array[0..128 - 1] of WideChar;
PLPCSTR = ^LPCSTR;
//https://learn.microsoft.com/en-us/windows/win32/api/wingdi/ns-wingdi-display_devicea
DISPLAY_DEVICE = packed record
cb: Cardinal;
deviceName: array[0..32 - 1] of WideChar;
deviceString: array[0..128 - 1] of WideChar;
stateFlags: Cardinal;
deviceID: array[0..128 - 1] of WideChar;
deviceKey: array[0..128 - 1] of WideChar;
end;
//https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-enumdisplaydevicesa
function EnumDisplayDevicesA(APCSTR: PLPCSTR; iDevNum: Cardinal; PDISPLAY_DEVICEA: PDISPLAY_DEVICE; dwFlags: Cardinal): BOOL; stdcall; external user32;
procedure PrintMonitorNames();
var
LDisplayDevice: DISPLAY_DEVICE;
LDeviceIndex: Integer;
LMonitorIndex: Integer;
LDeviceName: string;
begin
LDisplayDevice.cb := Sizeof(LDisplayDevice);
LDeviceIndex := 0;
while EnumDisplayDevicesA(nil, LDeviceIndex, #LDisplayDevice, 0) do
begin
LDeviceName := LDisplayDevice.deviceName;
Writeln('Device name: ' + LDeviceName);
LMonitorIndex := 0;
while EnumDisplayDevicesA(#LDeviceName, LMonitorIndex, #LDisplayDevice, 0) do
begin
Writeln(StrPas(LDisplayDevice.deviceName) + ' ' + StrPas(LDisplayDevice.deviceString));
Inc(LMonitorIndex);
end;
Inc(LDeviceIndex);
end;
end;
var
LDummy: string;
begin
Writeln('START');
PrintMonitorNames();
Writeln('FINISH');
Readln(LDummy);
end.

Answer 1

You are mixing ANSI and Unicode.
The EnumDisplayDevices function exists in two versions:
EnumDisplayDevicesA which is (legacy) ANSI.
EnumDisplayDevicesW which is Unicode.
You are calling the ANSI version EnumDisplayDevicesA, but are using a Unicode version of DISPLAY_DEVICE. So you need to use EnumDisplayDevicesW instead.
This phenomenon that an API function exists in both W and A versions is present everywhere in the Windows API, so the above remarks are very general.
The fact that you get Chinese text because of this encoding mismatch is also very well known.
Having said all this, you don't need to declare EnumDisplayDevices yourself at all. Everything you need is already present in the Delphi RTL's Windows.pas unit, just like I showed you two days ago:
program Project1;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils,
Winapi.Windows;
begin
var dd, md: TDisplayDevice;
FillChar(dd, SizeOf(dd), 0);
dd.cb := SizeOf(dd);
FillChar(md, SizeOf(md), 0);
md.cb := SizeOf(md);
var i := 0;
while EnumDisplayDevices(nil, i, dd, 0) do
begin
var j := 0;
while EnumDisplayDevices(#dd.DeviceName[0], j, md, 0) do
begin
Writeln(md.DeviceString);
Inc(j);
end;
Inc(i);
end;
Readln;
end.
Notice that MSDN says this:
The winuser.h header defines EnumDisplayDevices as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant.
The same remarks applies to the Delphi RTL's Windows.pas.