Inserting String Into StringBuilder Causes Runtime Error

Question

I am attempting to insert a string into a StringBuilder but I get a runtime error:

Exception of type 'System.OutOfMemoryException' was thrown.

Why is this happening and how can I fix this?

My code:

Branch curBranch("properties", "");
foreach (string line in fileContents) 
{
    if (isKeyValuePair(line))
       curBranch.Value += line + "\r\n"; // Exception of type 'System.OutOfMemoryException' was thrown.
}

Implementation of Branch

public class Branch {
    private string                      key         = null;
    public StringBuilder                _value      = new StringBuilder(); // MUCH MORE EFFICIENT to append to. If you append to a string in C# you'll be waiting decades LITERALLY
    private Dictionary <string, Branch> children    = new Dictionary <string, Branch>();

    public Branch(string nKey, string nValue) {
        key     = nKey;
        _value.Append(nValue);
    }

    public string Key {
        get { return key; }
    }

    public string Value {
        get 
        { 
            return this._value.ToString(); 
        }   
        set 
        {
            this._value.Append(value);
        }
    }
}

You are basically appending an entire copy of what you have in the stringbuilder with each call of curBranch.Value += line + "\r\n"; I don't think this is doing what you want it to do. — BlakeH
– BlakeH, Commented Jul 8, 2014 at 3:19

Grant Winney · Accepted Answer · 2014-07-08 03:19:05Z

5

This line returns the entire StringBuilder contents:

return this._value.ToString();

And then you add a string to the end of the entire previous contents:

curBranch.Value += line + "\r\n";

And append it here:

this._value.Append(value);

Your StringBuilder is going to get huge very quickly, because every time you call the "setter" you're placing a copy of the entire contents into it again.

What you might consider instead is exposing the StringBuilder via your property:

public StringBuilder Value
{
    get { return this._value; }   
}

Then just use it like this:

curBranch.Value.AppendLine(line);

answered Jul 8, 2014 at 3:19

Grant Winney

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2 Comments

sazr Over a year ago

thanks for the answer. Yes that solution would work. I was hoping for a more elegant solution that will allow the += operator. Any ideas how I could maintain using this operator but only concatenate the line (not the whole StringBuilder string and line)?

gretro Over a year ago

@JakeM You can always redefine the "+" operator. This would allow you to do what you want. Here is an example of how to proceed : msdn.microsoft.com/en-us/library/6fbs5e2h.aspx. However, I do recommend you use the AppendLine method as its meaning is not ambiguous and could hardly be more clear.

Community · Accepted Answer · 2017-05-23 12:05:44Z

2

StringBuilder sb = new StringBuilder();
foreach (string line in fileContents) 
{
    if (isKeyValuePair(line))
       sb.AppendLine(line); // Exception of type 'System.OutOfMemoryException' was thrown.
}

Try the above

I also found this explenation for why += isn't there for StringBuilder:

Why didn't microsoft overload the += operator for stringbuilder?

edited May 23, 2017 at 12:05

CommunityBot

11 silver badge

answered Jul 8, 2014 at 3:21

TGH

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