How do I print the help screen?

Issue by ptr727 Tuesday May 23, 2017 at 17:02 GMT _Originally opened as https://github.com/gsscoder/commandline/issues/445_

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How do I print the help output I’ve evaluated the logical options and something is wrong?

            // Parse the commandline arguments
            // https://github.com/gsscoder/commandline
            Parser parser = new Parser(with =>
            {
                with.CaseSensitive = false;
                with.HelpWriter = Console.Error;
            });
            ParserResult<Options> result = parser.ParseArguments<Options>(args);
            if (result.Tag == ParserResultType.NotParsed)
            {
                return -1;
            }
            Options options = ((Parsed<Options>)result).Value;

            // Process or monitor must be specified
            if (options.ProcessFolders == false && options.MonitorFolders == false)
            {
                // TODO : Call help output directly
                return -1;
            }

[ericnewton76]

Comment by veleek Tuesday Jul 25, 2017 at 23:23 GMT

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I believe that this is definitely a bug in the code. If you use the overload of AutoBuild(...) that takes onError and onExample functions then it will write successfully.

It actually has an explicit block in the code which checks whether or not the ParserResult<T> being passed in is a NotParsed result in which case it gracefully attempts to write the error output.

if (onError != null && parserResult.Tag == ParserResultType.NotParsed)
{
    errors = ((NotParsed<T>)parserResult).Errors;

    if (errors.OnlyMeaningfulOnes().Any())
        auto = onError(auto);
}

So, as a workaround in the meantime you can just use

Console.WriteLine(HelpText.AutoBuild(result, null, null));

[Kittyfisto]

The above workaround does not work for me (throws a NullReferenceException, using CommandLineParser 2.6.0), however only a simple change was needed to make it work:

Console.WriteLine(HelpText.AutoBuild(result, _ => _, _ => _));