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Have I got a console?
f#

Hi,

Following on from some comments by Tomas, re using Console.ReadLine to pause for input.

I wrote the following small function

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let pause =

    System.Console.WriteLine("Press a key to continue")

    System.Console.ReadKey)false) |> ignore

Fine, until, you invoke pause interactively, then the system stops and reports that there is no console, i.e.

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System.InvalidOperationException: Cannot read keys when either application does not have a console or when console input has been redirected from a file. Try Console.Read.

   at System.Console.ReadKey(Boolean intercept)

   at <StartupCode$FSI_0010>.$FSI_0010.main@() in C:\Users\joe\Documents\Visual Studio 2010\Projects\Six_Integers\Six_Integers\Program.fs:line 26

Stopped due to error

.

I've tried a try/with, try/finally with no joy.

How do I test for the presence of a console?

Many thanks

Joe

.

Hi,

First off thanks to both of you for replying.

Going backwards, easy to hard:

I am running purely under Win 7, VS2010 pro., freshly installed. I have cygwin. but I'm not using it with FSI.

I agree, OnorioCatenacci, that in a deployed system it would not matter, but in testing it does. Consider function A calls pause, and other higher functions call A. Then using a higher function results in an error.

BTW it makes no odds if pause is loaded into FSI directly.

Many Thanks

Joe

By on 6/26/2010 8:19 AM ()

BTW it makes no odds if pause is loaded into FSI directly.

I'm not quite sure I'm following you there Joe. I tried the example you posted in the FSI on my machine (Win 7 and VS 2010 as well) and it worked fine. I copy/pasted it into my FSI--if you "#load"ed it that might explain the difference.

When I said this wouldn't matter in a deployed system, I meant that when you build the .exe you'll specify that it's either a Windows subsystem executable (via the --target:winexe switch on fsc) or as a Console Subsystem executable (via the --target:exe switch). Hence if you actually need a console, you'd build it with the --target:exe switch and you'd get a console when the exe is started.

By on 6/26/2010 8:57 PM ()

I have a guess what has happened because I've had the same error message. Do you you use one of the standard cygwin terminals like rxvt, xterm or mintty. This won't work because these are not proper Win OS consoles but implemented by pipes, hence the error message. I this is the case and you want a nice terminal to use with fsi, I recommend Console2.

By on 6/25/2010 5:51 AM ()

Sorry to give you a "works on my machine" answer but . . . it works on my FSI. What happens if you try this code directly in FSI (vs. running it under VS 2010)? I'm going to hazard a guess that the VS2010 version is not running under the Windows console subsystem.

I should amplify a little I guess. If you were using this code in a production situation then you'd build the exe as a console exe. So I don't think there's really a need to test for a console; I think what you're seeing is just likely because of the way you're testing.

Hope that helps. :)

By on 6/23/2010 1:59 PM ()

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