CODEWITHSUNDEEP
delphiregistry
Christine Ross
Christine Ross

Reputation: 463

Can't read key from registry

I heared that Windows creates a unique key for a PC which is called "MachineID". I found two locations in my registry. Only the location "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography" should be correct. I try to read the value by this function:

    Function GetMaschineID:string;
var
Reg : TRegistry;

//HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger    =   {dd239a44-fa0d-43ff-a51c-5561d3e39de3}
//HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography   =   a06b0ee0-b639-4f55-9972-146776bcd5e4
begin
Reg := TRegistry.Create(KEY_READ);
try
Reg.Rootkey:=HKEY_LOCAL_MACHINE; //Hauptschlüssel
//Reg.RootKey:=HKEY_CURRENT_USER;
if Reg.OpenKey('SOFTWARE\Microsoft\Cryptography\',false) then //Unterschlüssel öffnen
//if Reg.OpenKey('Software\Microsoft\MSNMessenger\',false) then //Unterschlüssel öffnen
    begin
    Result:=Reg.ReadString('MachineGuid');
    end;
finally
     Reg.Free;
end;
end;

This version results in an empty string; you see as comment the result from the registry. The second version for "hkey_Current_user" brings the expected string result.

What is wrong with my code or are parts of the registry read protected?

Upvotes: 1

Views: 5901

Answers (2)

Mohamed Shahjahan
Mohamed Shahjahan

Reputation: 1

procedure TForm1.Button1Click(Sender: TObject);
var
    registry: TRegistry;
begin
    Registry := TRegistry.Create(KEY_READ OR KEY_WOW64_64KEY);
    try
        registry.RootKey := HKEY_LOCAL_MACHINE;
        if (registry.KeyExists('\SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL')) and
       (registry.OpenKeyReadOnly('\SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL')) then
        begin
            showmessage(registry.ReadString('SQLEXPRESS'));
            registry.CloseKey;
        end
        else showmessage('failed');
    finally
        registry.Free;
    end;
end;

Upvotes: -1

David Heffernan
David Heffernan

Reputation: 612794

Possible explanation 1

For HKLM you are subject to registry redirection. You have a 32 bit process and are trying to read a key from the 64 bit view of the registry. By default, your 32 bit process is redirected to the 32 bit view, which (implementation detail) lives under Wow6432Node.

Use the KEY_WOW64_64KEY access flag to read from the 64 bit view. As detailed here: How can I read 64-bit registry key from a 32-bit process?

Possible explanation 2

Your call to OpenKey fails for keys under HKLM because you are requesting write access and standard user does not have write access to HKLM. Use OpenKeyReadOnly instead.

Other advice

At the very least you should have debugged this a bit more. Does the call to Reg.OpenKey succeed or fail? You should have debugged enough to know that. Perhaps you did but did not say. If Reg.OpenKey failed then explanation 2 is most likely. Even then, you may subsequently suffer from the other problem.

Note also that your function does not assign to the function result variable, or raise an error, if the call to Reg.OpenKey fails. I would expect that the compiler would have warned you about that.

Upvotes: 8

Related Questions