4 replies to this topic

[Casper]

Hi all,

I think I found a bug in the recently added Regex library. Let's say we want a specific string from an AT string:

Debug.GC(true); // Force garbage collect

var regex = new Regex("\\+CUSD: 2,\"(.*?)\",0$"); // Our regular expression
var match = regex.Match("+CUSD: 2,\"Lorem ipsum dolor sit amet...\",0"); // The AT string

if (match.Success)
{
    Debug.Print(match.Groups[1].Value); // Print the result of the match
}

Debug.Print will correctly print: Lorem ipsum dolor sit amet...

But now the AT string is larger, let's say:

var match = regex.Match("+CUSD: 2,\"Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt...\",0");

When executed the output will say: "Failed allocation for 57 blocks, 684 bytes" and the string in match.Groups[1].Value is corrupted.

As you can see I force the garbage collector to run to ensure the full 40K RAM is available. Any ideas?

[Stefan W.]

Regexes can be really memory-heavy and slow, you just don't notice on desktop computers as much. If you anchor your regex and make the group atomic, it should work.

var regex = new Regex("^\\+CUSD: 2,\"(?>[^\"]*)\",0$"); // Our regular expression

[Stefan]

I just tested this code to the 4.2RC2 emulator:

using System;
using System.Threading;
using Microsoft.SPOT;
using Microsoft.SPOT.Hardware;
using SecretLabs.NETMF.Hardware;
using SecretLabs.NETMF.Hardware.Netduino;
using System.Text.RegularExpressions;

namespace NetduinoApplication1
{
    public class Program
    {
        public static void Main()
        {
            Debug.GC(true); // Force garbage collect

            var regex = new Regex("\\+CUSD: 2,\"(.*?)\",0$"); // Our regular expression
            //var match = regex.Match("+CUSD: 2,\"Lorem ipsum dolor sit amet...\",0"); // The AT string
            var match = regex.Match("+CUSD: 2,\"Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt...\",0");

            if (match.Success)
            {
                Debug.Print(match.Groups[1].Value); // Print the result of the match
            }
        }

    }
}

and it worked fine.

[Stefan W.]

Does the emulator have the memory constraints of a specific device?

[Stefan]

Does the emulator have the memory constraints of a specific device?

I hope so I can't test in RC2 on a netduino yet, since there's no rc2 firmware at this moment though.