C#: How to catch the exception when user refuses to grant elevated privileges?

Question

In my C# code I have roughly this:

    public void RunCommand()
    {
        var processStartInfo = new ProcessStartInfo(
            "notepad.exe")
        {
            UseShellExecute = true,
            Verb = "Runas",
        };
        var process = Process.Start(processStartInfo);
        process.WaitForExit(1000);
    }

When run, this prompts the user to grant elevated privileges. If the user refuses, the call throws a Win32Exception with the text "The operation was cancelled by the user".

I want to catch this exception specifically, i.e., tell it apart from other exceptions. I want to be able to know that the user has cancelled.

Can I be reasonably confident that when a Win32Exception is thrown, it is probably this? Or can the call throw Win32Exception for all sorts of other reasons? I don't want to start string matching on the error message, since that presumably varies depending on user settings...

It seems you have already tried it. Why should the exception type change? If it fails, does it really matter why it failed? I could think of other problems like FileNotFound, if `notepad.exe` is not available. — Thomas Weller, Jan 21 '20 at 09:48
I don't expect the exception type to _change_, but I expect that this call might throw **Win32Exception** for all sorts of other reasons. So if I catch **Win32Exception**, I'm not confident that it was due to user cancellation. — Claus Appel, Jan 21 '20 at 09:50
[Process.Start never returns when UAC denied](https://stackoverflow.com/q/23350175/7444103) — Jimi, Jan 21 '20 at 10:00
_"Check if the Win32Exception.ErrorCode is 1223 to be sure."_ - See also 0x0...4C7 (1223 in Hex) in [Win32 Error Codes](https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-erref/18d8fbe8-a967-4f1c-ae50-99ca8e491d2d) — Fildor, Jan 21 '20 at 10:02
That's the generic (`0x80004005`) *Access denied* exception (`HRESULT`). — Jimi, Jan 21 '20 at 10:06
What is the difference between 1223 and -2147467259? Do both of them indicate that the application failed to get elevated permissions? — Claus Appel, Jan 21 '20 at 10:10
The error codes are documented [here](https://learn.microsoft.com/en-us/windows/win32/debug/system-error-codes). `1223` is ERROR_CANCELLED. — Matthew Watson, Jan 21 '20 at 10:15
There's a macro to map a Win32 error to a `HRESULT`. It's probably in the documentation already linked (if you're interested) — Jimi, Jan 21 '20 at 10:44

score 1 · Accepted Answer · answered Jan 22 '20 at 11:37

I ended up doing this, which seems to work on my system:

    public void RunCommand()
    {
        var processStartInfo = new ProcessStartInfo(
            "notepad.exe")
        {
            UseShellExecute = true,
            Verb = "Runas",
        };
        var process = Process.Start(processStartInfo);
        process.WaitForExit(1000);
    }
    catch (Win32Exception e)
    {
        if (e.ErrorCode == 1223 || e.ErrorCode == -2147467259)
            // Throw easily recognizable custom exception.
            throw new ElevatedPermissionsDeniedException("Unable to get elevated privileges", e);
        else
            throw;
    }

C#: How to catch the exception when user refuses to grant elevated privileges?

1 Answers1