Question

Note: I am using Delphi XE2

I am trying to add a registry key. Here is my current code:

function AddRegKey(Key:HKEY;Keyname,Value:String):Boolean;
var
  phkResult:HKEY;
begin
  if RegOpenKeyEx(Key, PWideChar('SOFTWARE\Microsoft\Windows\CurrentVersion\Run'), 0, KEY_SET_VALUE, phkResult) = ERROR_SUCCESS then
    begin
      Result := (RegSetValueEx(phkResult, PWideChar(KeyName), 0, REG_SZ, PWideChar(Value), Length(Value)) = ERROR_SUCCESS);
      RegCloseKey(phkResult);
    end
  else Result:=False;
end;

begin
    If AddRegKey(HKEY_CURRENT_USER,'TestTest','123456789') Then
        MessageBox(0,'Success','Test',0);
end.

Which is resulting in the following:

It is only adding the first four characters

But when I change the “Value” parameter to:

123456789123456789

It then adds:

123456789

So it seems as if it is only adding half of the given value for some reason. How do I go about solving this?

Am I passing the wrong data type for the *lpData parameter in RegSetValueEx?

Answer 1

Read the documentation. The last parameter of RegSetValueEx() is a byte count, but you are passing it a character count instead (and not even the right count, either – you have to include the null terminator). SizeOf(WideChar) is 2, so you are telling RegSetValueEx() to write only half of the String data. You need to fix that, eg:

function AddRegKey(Key:HKEY; Keyname, Value: String): Boolean;
var
  phkResult: HKEY;
begin
  Result := False;
  if RegOpenKeyEx(Key, PChar('SOFTWARE\Microsoft\Windows\CurrentVersion\Run'), 0, KEY_SET_VALUE, phkResult) = ERROR_SUCCESS then
  begin
    Result := RegSetValueEx(phkResult, PChar(KeyName), 0, REG_SZ, PChar(Value), (Length(Value) + 1) * SizeOf(Char)) = ERROR_SUCCESS;
    RegCloseKey(phkResult);
  end;
end;

With that said, You might consider using the TRegistry class, which handles these details for you:

uses
  ..., Registry;

function AddRegKey(Key: HKEY; Keyname, Value: String): Boolean;
var
  Reg: TRegistry;
begin
  Result := False;
  try
    Reg := TRegistry.Create(KEY_SET_VALUE);
    try
      Reg.RootKey := Key;
      if Reg.OpenKey('SOFTWARE\Microsoft\Windows\CurrentVersion\Run', True) then
      try
        Reg.WriteString(KeyName, Value);
        Result := True;
      finally
        Reg.CloseKey;
      end;
    finally
      Reg.Free;
    end;
  except
  end;
end;