Stack overflow error in C# - but how to fix it?

Question

I've run into a really interesting runtime bug which generates a rogue stack overflow.

I've defined a structure as follows:

public enum EnumDataType { Raspberry, Orange, Pear, Apple };

public class DataRequest
{
    public long DataSize 
    { 
        get { return 0; } 
        set { DataSize = value; } 
    }

    public EnumDataType DataType  
    { 
        get { return EnumDataType.Apple; } 
        set { DataType = value; } 
    }
}

The following lines work perfectly:

DataRequest request = new DataRequest();
request.DataSize = 60;

However, when I step over the following line in code, it generates a stack overflow:

request.DataType = EnumDataType.Raspberry;

Of course, I can fix it by removing the defaults, or using auto get/set, but I need it to be both readable and writable, and return a default - any ideas?

I would expect invoking either of those setters to cause a stack overflow, whatever value you supplied. Perhaps you could offer a short but complete program to demonstrate the first one "[work]ing perfectly" ? — AakashM
– AakashM, Commented Oct 27, 2010 at 13:49
I've always found Stackoverflow errors to be quite amusing errors when they crop up, since the few times I have seen them they usually involve two or more methods that are beautifully named inverses of each other. Instead of containing any functional code they reference each other, which would be so wonderful if it worked, but nope. The future has yet to come. — WonderWorker
– WonderWorker, Commented Sep 30, 2016 at 8:06

Neil Knight · Accepted Answer · 2010-10-27 13:45:54Z

20

public long DataSize { get { return 0; } set { DataSize = value; } }

You are constantly setting the value of DataSize. You need to create a local variable and use that instead. e.g.

private long dataSize;

public long DataSize
{
    get { return this.dataSize; }
    set { this.dataSize = value; }
}

EDIT I've written DataSize but the same applies to DataType

edited Oct 27, 2010 at 13:45

answered Oct 27, 2010 at 13:36

Neil Knight

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6 Comments

John Nicholas Over a year ago

+8 but no explanation of why the stack overflow occurs?

Jon Skeet Over a year ago

-1: This will still always return 0 instead of just making 0 the default value. Admittedly the question isn't clear, but I don't think it's what was meant.

Spoike Over a year ago

@John Nicholas: That is because the program is trying to set DataSize with DataSize, that in turn wants to set it's DataSize with DataSize, which will set that one's DataSize with DataSize. And then it will set it's DataSize with DataSize, after that it will set the DataSize with DataSize… Whew, mindblowing; and I'm not even half-way there!

John Nicholas Over a year ago

I know why ;) the origional asker didn't though ;)

Contango Over a year ago

Thanks - great answer. I understand exactly whats going on now. We're not dealing with properties, we're dealing with methods, as its an object.

|

Jon Skeet · Accepted Answer · 2010-10-27 13:45:50Z

14

As others have said, the stack overflow occurs because your property setter is just calling itself. It may be simpler to understand if you think of it as a method:

// This obviously recurses until it blows up
public void SetDataType(long value)
{
    SetDataType(value);
}

As I understand it, you're trying to create normal properties but with a default value, right?

In that case, you need backing variables which are set by the setters - and the getters should return those variables, too. It's the variables which should get default values:

private long dataSize = 0;
public long DataSize {
  get { return dataSize; }
  set { dataSize = value; }
}

private EnumDataType dataType = EnumDataType.Apple;
public EnumDataType DataType { 
  get { return dataType; }
  set { dataType = value; }
}

Alternatively, use automatic properties but set the defaults in your constructor:

public long DataSize { get; set; }
public EnumDataType DataType { get; set; }

public DataRequest()
{
    DataSize = 0; // Not really required; default anyway
    DataType = EnumDataType.Apple;
}

edited Oct 27, 2010 at 13:45

answered Oct 27, 2010 at 13:36

Jon Skeet

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1 Comment

Contango Over a year ago

Thanks - great answer. I understand exactly whats going on now. We're not dealing with properties, we're dealing with methods, as its an object. The reason behind my original question was how to set the defaults that are returned, and your answer covers this. p.s. Enjoyed your talk in London at the start of this year - your presentation was genuinely interesting, and not just because of the sock puppets :)

John Nicholas · Accepted Answer · 2010-10-27 13:39:02Z

stack overflow happens because in the setter you are setting the property to a value (Ie you are trying to get something to set itself to something ... which causes an infinite loop) ... which means that it tries to set itself to a value which means its tries to set itself to a value untill boom

your properties will never get the values you are setting because they always return the same value (not the stored value)

public enum EnumDataType { Raspberry, Orange, Pear, Apple }; 

public class DataRequest 
{ 
private long _dataSize = 0;
private EnumDataType _dataType = EnumDataType.Apple;

public long DataSize { get { return _dataSize ; } set { _dataSixe= value; } } 
public EnumDataType DataType  { get { return _dataType; } set { _dataType= value; } } 
}

is what you really wanted

Tokk · Accepted Answer · 2010-10-27 13:47:07Z

3

you have to implemet it with a backing store:

private EnumDataType dataType;
public EnumDataType DataType  { get { return EnumDataType.Apple; } set { dataType = value; } }

}

You should do so anytime you do some acion in the getter and setters. By the way, why can you even set the variables? you can't read them out, you always get EnumDataType.Apple. If you want a start value, you can do like this:

private EnumDataType dataType = EnumDataType.Apple;
public EnumDataType
{
   get
   {
       return dataType;
   }
   set
   {
       dataType = value;
   }
 }

edited Oct 27, 2010 at 13:47

answered Oct 27, 2010 at 13:36

Tokk

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1 Comment

Jon Skeet Over a year ago

That won't compile - EnumDataType is a non-nullable value type.

Dave Bish · Accepted Answer · 2010-10-27 13:37:35Z

2

I don't understand how the first line: request.DataSize = 60;

Doesn't cause a stack overflow - my advice would be to use backing properties:

public class DataRequest
{
    protected int dataSize = 0;
    protected EnumDataType enumDataType;
    public long DataSize { get { return 0; } set { dataSize = value; } }
    public EnumDataType DataType  { get { return EnumDataType.Apple; } set { enumDataType = value;} 
}

answered Oct 27, 2010 at 13:37

Dave Bish

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