c# HttpWebRequest Timeout setting to zero

Yes, it will timout immediately, you can test it yourself easily:

try
{
    WebRequest myWebRequest = WebRequest.Create("http://stackoverflow.com/questions/38340099/c-sharp-httpwebrequest-timeout-setting-to-zero");
    myWebRequest.Timeout = 0;
    WebResponse myWebResponse = myWebRequest.GetResponse();
}
catch (Exception ex)
{
    Console.WriteLine(ex.Message); // timeout exceeded
}

Why? I've asked myself the same. Maybe for testing purposes or if you need a default value that clearly doesn't work accidentially to ensure that the property will be set in any case.

Interestingly negative values aren't allowed apart from -1, since that is the value of System.Threading.Timeout.Infinite. Here's the source:

public override int Timeout {
    get {
        return _Timeout;
    }
    set {
        if (value<0 && value!=System.Threading.Timeout.Infinite) {
            throw new ArgumentOutOfRangeException("value", SR.GetString(SR.net_io_timeout_use_ge_zero));
        }
        if (_Timeout != value)
        {
            _Timeout = value;
            _TimerQueue = null;
        }
    }
}