Know when variables inside a struct become null in Visual Studio?

Question

I have a struct on the server-side with a layout like this:

struct SomeStruct
{
    public string SomeString { get; set; };
    public string SomeString1;
    public string SomeString2;
    public string SomeString3;
}

I am using a client/server model, and an instance of this struct gets referenced a lot of times as it has really important information (over 200 times).

The thing is that when some function gets called, the values inside this struct become null. I don't know why and it is been bugging me for a really long time.

I call a lot of methods before realizing that this values are null, so I don't know which section of my code nullify my strings.

I am using VS2012, but I have 2010 and 2008 ultimate as well. I was wondering if there is a way to perform a trigger when some section of code nullifies my strings.

I tried to add some properties like this, bot the exception was never thrown:

struct SomeStruct {
    string somestr;
    public string SomeString
    {
        get { return somestr; }
        set
        {
            if (value == null)
            {
                throw new Exception("stirng is null");
            }

            somestr = value;
        }
    }
    public string SomeString1;
    public string SomeString2;
    public string SomeString3;
}

Might not be important, but this is one of the structs I am using (the Name variable becomes null in some part of my code, and the rest turns into default()):

[ProtoContract]
public struct CharacterInformation
{
    [ProtoMember(2)]
    public string Name;
    [ProtoMember(3)]
    public IntegerVector2 Position;
    [ProtoMember(5)]
    public CharacterDirection Direction;
    [ProtoMember(6)]
    public CharacterStatus Status;
    [ProtoMember(7)]
    public CharacterClass Class;
    [ProtoMember(8)]
    public CharacterRace Race;
    [ProtoMember(9)]
    public CharacterType Type;
    [ProtoMember(10)]
    public CharacterFaction Faction;
    [ProtoMember(11)]
    public float MovementModifier;
    [ProtoMember(12)]
    public CharacterEquipment Equipment;
}

Edit: The only instance of this struct is created on a Sql-related function:

public CharacterServerInformation GetInformation(int charID)
        {
            CharacterServerInformation information = new CharacterServerInformation();
            if (!authInstance.CharacterExists(charID))
            {
                // char doesn't exists
                throw new Exception("Character doesn't exists");
            }
            information.ID = charID;
            information.Experience = GetExperience(charID);
            information.Info.Direction = CharacterDirection.Bottom;
            information.Info.Name = authInstance.CharacterGetName(charID);
            information.Info.Class = GetClass(charID);
            information.Info.Faction = GetFaction(charID);
            information.Info.Position = GetPosition(charID);
            information.Info.Race = GetRace(charID);
            information.Info.Status = GetStatus(charID);
            information.Info.Type = GetType(charID);
            information.Info.MovementModifier = 1f; // should store old movement modifier, but well, whatever
            information.HealthLeft = GetHealthLastLogout(charID);
            return information;
        }

Can you show how you are creating and using instances of the struct? — hatchet - done with SOverflow, Oct 05 '12 at 23:24
Simple debug version: throw `ArgumentException` if something happens to set it to null? I haven't done much with C# (yet), but isn't modifying internal struct values recommended against? — Clockwork-Muse, Oct 05 '12 at 23:24
@Clockwork-Muse - yes..OP should read this http://stackoverflow.com/questions/441309/why-are-mutable-structs-evil — hatchet - done with SOverflow, Oct 05 '12 at 23:27
Should I change all my structs to classes? If they have mutable data* — Pacha, Oct 05 '12 at 23:30
@Pacha - this http://stackoverflow.com/questions/521298/when-to-use-struct-in-c may help answer your question about struct vs. class. — hatchet - done with SOverflow, Oct 05 '12 at 23:33
@Pacha I think so. For performance issues and bug-prevention (since structs are passed by value not by reference) — , Oct 05 '12 at 23:35
You might be right. I am really new to programming, I still make silly mistakes. Didn't know about this. I thought that structs should contain data and classes functionality. — Pacha, Oct 05 '12 at 23:36
Putting code to notify if a setter is called with a null value might not help. The struct may be getting nullified because you're assigning `_s = new SomeStruct();` somewhere by mistake. The property setters won't get called here, but the underlying fields will be null. — phoog, Oct 05 '12 at 23:38

score 4 · Accepted Answer · answered Oct 05 '12 at 23:33

I suspect the problem is purely because you're using struct and not making a class. Since struct members are copied by value into methods and when returned from methods, including property getters, it's likely that you're "losing" the information by accidentally writing a new struct somewhere.

In this case, class seems is far more appropriate. If you read Choosing Between Classes and Structures, you'll see that struct should only be used when:

It logically represents a single value, similar to primitive types (integer, double, and so on).
It has an instance size smaller than 16 bytes.
It is immutable.
It will not have to be boxed frequently.

In your case, all of these criteria ( except maybe the last) are being violated, so class would be more appropriate.

Out of curiosity why the smaller than 16 bytes recommendation? Why not 32 for example? — Jared, Oct 05 '12 at 23:37
@Jared Very good reason why 16 bytes was choosen. See: http://stackoverflow.com/a/2437938/65358 — Reed Copsey, Oct 05 '12 at 23:46

Know when variables inside a struct become null in Visual Studio?

1 Answers1