How to open a registry key for reading data without requesting write access

Problem/Question/Abstract:

How can an application open a registry key for reading data without requesting write access? TRegistry seems to open keys always for ReadWrite, which fails on WindowsNT if the user has no write permission on that key (which is the default for HKEY_LOCAL_MACHINE if the user is no Administrator). I want to write user independant registry data into HKEY_LOCAL_MACHINE during installation (which is supposed to be the standard according to the WIN API Help) and have the program, which is normally not run by an administrator, to read these data on startup.

Since everything in TRegistry is static - as always when I want to inherit from a VCL anchestor - I cannot simply write a descendant of TRegistry that overrides the OpenKey and GetKey methods. Do I have to patch the source or to copy and modify the whole TRegistry code or am I missing something obvious?

Answer:

Alternatively you can directly use the Win32API calls:


{Local. Read the registry for the given key}

function GetKeyValue(const key: string): string;
var
  hkey: THandle;
  buf: array[0..255] of Char;
  n: Longint;
begin
  Result := '';
  if regOpenKeyEx(HKEY_CLASSES_ROOT, @key[1], 0, KEY_READ, hKey) = ERROR_SUCCESS then
  begin
    n := 255;
    if regQueryValue(hKey, nil, buf, n) = ERROR_SUCCESS then
    begin
      Result := StrPas(buf);
    end;
    RegCloseKey(hkey);
  end
  else
    Result := '';
end;

{Local. Look through the Registry looking for the descriptions of the given extension.}

function GetDescription(Extension: string): string;
var
  intermediate: string;
begin
  {Get intermediate value}
  intermediate := GetKeyValue(Extension);
  if intermediate <> '' then
  begin
    {Look up definition for the full description}
    Result := GetKeyValue(intermediate);
  end
  else
    Result := '';
end;

{Local. Read the registry for the description of the given file extension.}

function getExtensionDescription(const extension: string): string;
var
  description: string;
begin
  {Try to get the description from the registry}
  description := GetDescription(extension);
  {Make sure we have a description to present to the user}
  if description = '' then
    description := extension + ' file';
  {Return the description to the caller}
  Result := description;
end;