PowerShell and WinApi

user_10767014 0
Viewed 190

I was trying this:

$signature = @'
[DllImport("shell32.dll")]
public static extern int ShellExecuteW(
  int    hwnd,
  string lpOperation,
  string lpFile,
  string lpParameters,
  string lpDirectory,
  int     nShowCmd
);
'@

$exec = Add-Type -memberDefinition $signature -name "win" -namespace Win32Functions -passThru

$exec::ShellExecuteW(0, "open", "notepad.exe", 0, 0, 1)

but the notepad does not start. How do I write this down correctly?

winapi powershell
1 Answers

The immediate fix is twofold:

  • [DllImport("shell32.dll")] ->
    [DllImport("Shell32.dll", CharSet = CharSet.Unicode)]

    • Since you explicitly target ShellExecuteW - the Unicode version of the API function - you must declare that fact via the CharSet field in the attribute. Once you do, you could actually omit the W suffix.[1]

    • int hwnd must be IntPtr hwnd.

  • $exec::ShellExecuteW(0, "open", "notepad.exe", 0, 0, 1) ->
    $exec::ShellExecute(0, "open", "notepad.exe", [NullString]::Value, [NullString]::Value, 1)

    • Note the use of [NullString]::Value to pass null to the string-typed parameters; by default, PowerShell treats $null in a string context as the empty string rather than null; in this particular case, however, the empty string (and therefore $null) would work too.

To put it all together:

$exec = Add-Type -name "win" -namespace Win32Functions -passThru -memberDefinition @'
[DllImport("shell32.dll", CharSet=CharSet.Unicode)]
public static extern int ShellExecuteW(
  IntPtr hwnd,
  string lpOperation,
  string lpFile,
  string lpParameters,
  string lpDirectory,
  int    nShowCmd
);
'@

$exec::ShellExecuteW(
  0, 
  'open', 
  'notepad.exe', 
  [NullString]::Value, 
  [NullString]::Value, 
  1
)

Taking a step back: The Start-Process cmdlet allows you to do the same without the need for on-demand-compiled P/Invoke declarations:

# Use -WorkingDirectory, if  needed.
Start-Process Notepad.Exe -Verb Open -WindowStyle Normal

[1] Omitting the W suffix (ShellExecute) while not specifying a CharSet value defaults to the ANSI version of the function. Using the W suffix alone - without CharSet=CharSet.Unicode - is not enough.

user_453750
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