QSysInfo::machineUniqueId() empty on Windows

[Marek]

Hi
Since Qt 5.11 there is function QSysInfo::machineUniqueId() which should return unique ID per machine (eg. processor number, mainboard number), on Linux it works, on Windows 10 it returns empty string (tested on Win 10 and Qt 5.11.1).
Is this as it should be ? Can't get this machineUniqueId on Windows, or is this some bug?

Best Regards
Marek

[JonB]

@Marek
I suspect this is because from docs:

QByteArray QSysInfo::machineUniqueId()
See also machineHostName() and bootUniqueId().

and

QByteArray QSysInfo::bootUniqueId()
This function is currently only implemented for Linux and Apple operating systems.
See also machineUniqueId().

EDIT: Hmm, maybe not. From https://code.woboq.org/qt5/qtbase/src/corelib/global/qglobal.cpp.html#_ZN8QSysInfo15machineUniqueIdEv I see:

#elif defined(Q_OS_WIN) && !defined(Q_OS_WINRT) 
    // Let's poke at the registry 
    HKEY key = NULL; 
    if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Microsoft\\Cryptography", 0, KEY_READ, &key) 
            == ERROR_SUCCESS) { 
        wchar_t buffer[UuidStringLen + 1]; 
        DWORD size = sizeof(buffer); 
        bool ok = (RegQueryValueEx(key, L"MachineGuid", NULL, NULL, (LPBYTE)buffer, &size) == 
                   ERROR_SUCCESS); 
        RegCloseKey(key); 
        if (ok) 
            return QStringView(buffer, (size - 1) / 2).toLatin1(); 
    } 
#endif 
    return QByteArray(); 

So, assuming not Q_OS_WINRT (whatever that is for), do you have that registry value defined, and readable to your app?

[Marek]

@JonB I will try this now, but since RegOpenKeyEx is from Win api not Qt which lib should I link to and include headers?

Thanks,
Marek

[JonB]

@Marek
Not sure what you mean, but I did not mean compile anything! I meant: look at that code, and go look in your registry to see whether you even have that entry sitting there or not, because that is the code Qt will be executing for you. I can see that key value under my Win 8 (so I would expect the Qt call to work), maybe it isn't there on your machine in Win 10, or (unlikely?) your Qt app process has no permission to read it from the registry?

[Marek]

@JonB I have compiled this into app and it returns empty string, I think because I can see Q_OS_WINRT is set
This windows is a bit slow...

[JonB]

@Marek
http://qt.apidoc.info/5.2.0/qtcore/qtglobal.html#Q_OS_WINRT:

Defined for Windows Runtime (Windows Store apps) on Windows 8, Windows RT, and Windows Phone 8.

Is your Qt compiled for Win 10 "Windows Store app" ??

[Marek]

@JonB No I'm using QtIFW to create installer

[JonB]

@Marek

• Recheck your claim "I think because I can see Q_OS_WINRT is set", because that doesn't sound likely to me?
• Look in your registry to see what you have for the key entry referenced in the code?

[Marek]

@JonB Yeah, I have downloaded some tool for registry and I'm checking, will report

[JonB]

@Marek
You don't need to download anything, you already have REGEDIT! :)

[Marek]

@JonB REGEDIT inside Win ? Sorry I don't work usally on Windows. I have downloaded some regmagik and I can see that Microsoft\Cryptography hasn't any keys only some branches.

[Marek]

@JonB I have searched through the registry and there is no MachineGuid in reg

[JonB]

@Marek
Yeah, everybody knows that Windows comes with REGEDIT for examining the Registry! :)

If you don't have HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\MachineGuid (I do), that function is not going to return anything on your machine. That's all I know.

[Marek]

@JonB anyway thanks for help, I really have Q_OS_WINRT set thats why this code returned empty string first time I have compiled

[JonB]

@Marek
Well actually that sounds more reasonable as an explanation, because I think the registry entry really is there under all Windows.

Now your question becomes: "why does the Qt I am using seem to have been compiled with Q_OS_WINRT defined, because I would have thought it should not?".

I am not a Qt expert: you would need someone like @SGaist to see this, look through my understanding of what must be going on, and explain.

[Marek]

@JonB does this matter if on my win 10 there is o MachineGuid key ?
I'm checking something, I'm using MinGW 32 bit, https://github.com/gentoo90/winreg-rs/issues/10 try to compile with msvc2017 64bit

[Marek]

@JonB OK, success, Thanks for your help ;)
so windows can provide "virtual" registry for 32 bit applications and this registry does not have MachineGuid. I have compiled with msvc2017 64Bit and it works. I can call it a day ;)

Best,
Marek

[JonB]

@Marek
Yes it can. It's all to do with the Wow6432Node key:

Yes, for 32-bit software 64-bit OS will substitute HKLM\SOFTWARE\ path with HKLM\SOFTWARE\Wow6432Node\. So you were trying to read HKLM\SOFTWARE\Wow6432Node\Microsoft\Cryptography\MachineGuid which doesn't exist.

You did not say in your question that any 32-bitted-ness was involved at your side, I assumed all 64-bit, else I would have said about needing to change where you look in the registry :)

[Marek]

@JonB I did not supposed it matters, frankly I prefer to use MinGW (old habits maybe) and I didn't see Qt 5.11 for MinGW 64bit.
@CoreyAnderson how this HP printer support is related to Qt or even Windows 10, I don't get it, you mean bug in Windows that it does not provide key for 32bit apps ?

[JonB]

@Marek

Ignore @CoreyAnderson 's post, he is just advertising his hyperlink! It's a scam.

You can use a 64-bit compiler with no issue. If you want to use a 32-bit compiler, you will have to do some work.