fcl-registry

fcl-registry is an FCL unit that provides access to the Windows registry. It is cross-platform. How? In non-Windows operating systems it creates a reg.xml file. For example, under non-Windows operating systems it creates the per user XML file (HKEY_CURRENT_USER) reg.xml in the /home/[user]/.config/application_name/ directory; the global XML file (HKEY_LOCAL_MACHINE) reg.xml is created in the /etc/application_name/ directory which is invariably a read-only location unless you are the root or Admin user.

Registry terms

RootKey: registry hive where you want to start accessing the registry. Examples: HKEY_LOCAL_MACHINE, HKEY_CURRENT_USER

Key: the path to the "directory" that contains individual data. This is a bit counter-intuitive but a holdover from compatibility with earlier versions of the registry.

Name/value: the actual name/value pairs in the Key "directory". Each key can have a default value, whose name is (an empty string).

Example

Example that tries to get a value:

uses ... registry...

var
  CompileCommand: string='';
  Registry: TRegistry;
begin
  Registry := TRegistry.Create;
  try
    // Navigate to proper "directory":
    Registry.RootKey := HKEY_LOCAL_MACHINE;
    if Registry.OpenKeyReadOnly('\SOFTWARE\Classes\InnoSetupScriptFile\shell\Compile\Command') then
      CompileCommand:=Registry.ReadString(''); //read the value of the default name
  finally
    Registry.Free;  // In non-Windows operating systems this flushes the reg.xml file to disk
  end;
end;

Accessing 64 bit and 32 bit registry views

If you have 64 bit Windows, the registry is split up into a 64 bit and 32 bit (compatibility) part. By default, if you run a 32 bit process, you see the 32 bit part; if you run a 64 bit application, you see the 64 bit part.

You can also access the 32 bit part from 64 bit applications and vice versa. From MSDN

• KEY_WOW64_64KEY: Access a 64-bit key from either a 32-bit or 64-bit application.
• KEY_WOW64_32KEY: Access a 32-bit key from either a 32-bit or 64-bit application.

These keys are defined in the registry unit so you can just use them: eg in the registry object's Access property, like this:

Registry := TRegistry.Create;
Try
  Registry.Access:=Registry.Access or KEY_WOW64_64KEY;

or in the registry.create call, eg:

TRegistry.Create(KEY_READ or KEY_WOW64_64KEY);

Administrative privileges

Depending on what you want to read/write in the Windows registry, you may need administrator rights and elevation (Windows Vista+). Please see Use manifest file to set execution level

See also

Packages List

From the Free Pascal wiki, page "fcl-registry", as it stood on 2020-05-06 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.