DateTime.ToString in Mono return invalid date (“00

问题:

I am trying to get mono (Debian 2.10.8.1-5) to run properly on my raspberry pi with the raspbian distro ("Debian GNU/Linux wheezy/sid"). I have installed mono with apt-get install mono-complete.

However, I am running into an interesting issue that I cannot figure out. The DateTime.ToString() method returns an invalid string.

Below you can find my sample program with the console output:

using System;

namespace MonoTest
{
    class Program
    {
        static void Main(string[] args)
        {
            DateTime now = DateTime.Now;
            Console.WriteLine("Year: " + now.Year);
            Console.WriteLine("Month: " + now.Month);
            Console.WriteLine("Day: " + now.Day);
            Console.WriteLine("DayOfWeek: " + now.DayOfWeek);
            Console.WriteLine("DateTime.Now: " + DateTime.Now);
            Console.WriteLine(DateTime.Now.ToString("yyyy-MM-dd"));
        }
    }
}

Output:

pi@raspberrypi ~/bin $ mono MonoTest.exe
Year: 2012
Month: 8
Day: 3
DayOfWeek: Friday
DateTime.Now: 00/734718/0001 01:41:38
0001-00-734718

Interestingly enough, 734718 seems to be the the number of days elapsed till today since 01/01/0001. I have tryed it with a fresh installation on a second board but with the same issue.

Does anyone have an idea what the problem here is and how to convince DateTime.ToString() to return the right value?

Update (8/4/2012): After long digging through the mono source code I was able to trace the issue back to System.Math.Floor. Apparently, it always returns 0. I changed my test program to a simple:

static void Main(string[] args)
{
    Console.WriteLine("Floor(1.5): " + System.Math.Floor(1.5));
}

On Windows the result is "Floor(1.5): 1" Whereas on my mono setup on the raspberry pi is "Floor(1.5): 0". I have seen that System.Math.Floor is implemented as

[MethodImplAttribute (MethodImplOptions.InternalCall)]
public extern static double Floor (double d);

Tomorrow, I will look further into this issue. Does anyone know why this issue could exist?

回答1:

This is Mono bug #7938, and it affects not just DateTime.ToString, but ANY function that, directly or indirectly, passes a floating-point number to a library call, when running on ARM with a Linux distro built for the hard-float ABI. More details are available at the C# on Raspberry Pi wiki page. There is currently no good fix for this, short of running a soft-float distro. I'm still hoping we can get a fixed mono runtime soon.

回答2:

I can't reproduce your issue on Windows (don't have raspberry, but your subject says Mono).

I copied and pasted your exact source for Main() into a new Mono console app (Mono 2.6.1), added a single line (Console.ReadLine();), and ran it:

using System;

namespace TestDateTimeNow
{

  class MainClass
  {
    public static void Main (string[] args)
    {
        DateTime now = DateTime.Now;
        Console.WriteLine("Year: " + now.Year);
        Console.WriteLine("Month: " + now.Month);
        Console.WriteLine("Day: " + now.Day);
        Console.WriteLine("DayOfWeek: " + now.DayOfWeek);
        Console.WriteLine("DateTime.Now: " + DateTime.Now);
        Console.WriteLine(DateTime.Now.ToString("yyyy-MM-dd"));
        Console.ReadLine();
    }
  }
}

I get the output below:

回答3:

That's most likely to be an ARM Mono binary layer bug. Especially since you are running a version that was release before Raspberry Pi. You will have much better luck with that on mono-devel mailing list. And it's possible that this is fixed in git already.

回答4:

You need to use the soft floating point OS for this. 2013-05-29-wheezy-armel.zip for example.

The hard floating point doesn't work well with JITers. I had the same issue, resolved it by installing the soft floating point version of the OS on my RP. I wouldn't recommended using .net with a hard floating point OS under the raspberry pi platform. Hope this helps.