Will instantiating a lot of variables (string, int, etc.) consume a lot of memory?

I've been thinking of making my code more readable. I have a lot of foreach and for loops since I handle lots of DataTables in my code.

Is it okay if I instantiate column names that I will use inside loops? Or will it consume too much memory? For example:

DataTable fooTable = new DataTable();

foreach(DataRow dr in fooTable.Rows)

string nameColumn = dr.Field<string>("NAME")
Console.WriteLine(nameColumn)



vs.

DataTable fooTable = new DataTable();

foreach(DataRow dr in fooTable.Rows)

Console.WriteLine(dr.Field<string>("NAME"))



DataTable

3 Answers
3

It's likely (certainly in debug mode) that there's an unnamed local variable used to store the result of dr.Field<string>("Name") in the version where you don't name a variable.

dr.Field<string>("Name")

And even then, the variable exists once in this method. You don't get a new variable each time through the loop.

Memory is allocated when you instantiate an object, not when you reference it. Thus no matter how many references to the same instance you have, the memory won´t increase.

This means the following two lines are identical considering their memory-footprint:

MyClass a = new MyClass();
Console.WriteLine(a);


and

Console.WrileLine(new MyClass());


in both cases there´s exactly one single instance of your class, not two. Thus the memory-consumoption is exactly that for one instance of the class (plus some small amount for the references theirselves, on a 32bit machine that´s 4bytes, on 64bit 8byte).

In your case memory is allocated when calling dr.Field<string>("NAME"). However in your first code the object is referenced, thus it may be garbage-collected some nano-seconds later (when the loop is on the next iteration).

dr.Field<string>("NAME")

Having said this it´s very unlikely that your memory increases much (if at all) when you have a million references all referencing the exact same object.

You should definitely use a temporary variable like nameColumn whenever you are in this kind of situation.

nameColumn

Each time you call dr.Field<string>("NAME"), the runtime has to construct an iterator and execute a string matching algorithm on a collection of objects just to find the right field to access. The amount of overhead caused by accessing the Field method far exceeds whatever impact may be caused by the temporary variable.

dr.Field<string>("NAME")

Field

So if you ever plan to use nameColumn in more than one place, the variable is what you need. Even if you don't re-use it, putting it in at the beginning is not a bad practice.

nameColumn

Adding the variable is not likely to have any negative impact. The compiler may even end up generating the same IL anyway.

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