Delphi - On Screen Keyboard (osk.exe) works on Win32 but fails on Win64

delphi, delphi-xe, wow64

Solution

There is something special about osk under UAC. This code fails with error code 740, `ERROR_ELEVATION_REQUIRED`, The requested operation requires elevation.

var
  si: TStartupInfo;
  pi: TProcessInformation;
....
si.cb := SizeOf(si);
GetStartupInfo(si);
Win32Check(CreateProcess('C:\Windows\system32\osk.exe', nil, nil, nil, 
  False, 0, nil, nil, si, pi));

This fails under both 32 and 64 bit processes on machines with UAC. You can find some discussion of the issue here: https://web.archive.org/web/20170311141004/http://blog.delphi-jedi.net/2008/05/17/the-case-of-shellexecute-shellexecuteex-createprocess-and-oskexe/

So your problem is not related to 32 or 64 bit, rather it is down to your XP system not having UAC.

More broadly I think this should be enough to convince you never to call `ShellExecute` again. It only exists for 16 bit compatibility and is singularly useless at reporting errors. If you want errors call `ShellExecuteEx`. However, since we are starting a new process, `CreateProcess` would normally be the right API to call.

That said, in this specific case the design of osk is such that it cannot be started programmatically by `CreateProcess`. It does need to be invoked by `ShellExecute`, or `ShellExecuteEx`. This allows the shell to perform its UAC magic. Now, it turns out that magic cannot happen from a 32 bit WOW64 process. The solution then is to start osk from a 64 bit process with a call to `ShellExecuteEx`.

Here is your workaround:

- On a 32 bit system, you can simply call `ShellExecuteEx` to open `osk`.

- On a 64 bit system, if your process is 64 bit, you can again call `ShellExecuteEx` to open `osk`.

- On a 64 bit system, if your process is 32 bit WOW64 process, you need to start a separate 64 bit process which in turn calls `ShellExecuteEx` to open `osk`.

Since you don't appear to be using a 64 bit version of Delphi, you'll need to find a 64 bit compiler. You could use the 64 bit fpc, or a 64 bit C++ compiler. The following C++ program is enough:

#include <Windows.h>
#include <Shellapi.h>

int CALLBACK WinMain(
  HINSTANCE hInstance,
  HINSTANCE hPrevInstance,
  LPSTR lpCmdLine,
  int nCmdShow
)
{
    SHELLEXECUTEINFOW sei = { sizeof(sei) };
    sei.lpVerb = L"open";
    sei.lpFile = L"osk.exe";
    sei.nShow = SW_SHOW;
    ShellExecuteExW(&sei);
}

You can compile that with a 64 bit C++ compiler and then call it from your 32 bit WOW64 process. Long winded I know, but it does have the merit of actually working!

Problem

Original source