CODEWITHSUNDEEP
c#class
DarthVegan
DarthVegan

Reputation: 1269

Passing a copy of a class is altering the original copy

I have some code that downloads data into a class for storage and then creates a copy of that class to pass into a method that alters the data. Somehow my original class is also being altered and I'm not sure what I'm doing wrong.

Calculations calc = new Calculations(Symbol, Market);
calc.stockData = loadData(Symbol, Market);
for (int j = calc.stockData.Count - 8; j >= 0; j--)
                    {
                        highPrice = 0;

                        // 0 newest
                        // as you go higher in the index, it is older
                        for (int k = j + 1; k < j + 8; k++)
                        {
                            kIndex = k;
                            jIndex = j;
                            decimal highRiskCurrentHigh = Calculations.calculateReturnPercentageStatic(calc.stockData.ElementAtOrDefault(k).Close,
                                calc.stockData.ElementAtOrDefault(j).High);

                            if (highRiskCurrentHigh > highPrice)
                            {
                                highPrice = highRiskCurrentHigh;
                                highIndex = k;
                            }
                        }

                        Test test = new Test();
                        test.returnPct = highPrice;
                        test.date = calc.stockData.ElementAtOrDefault(highIndex).Date;
                        test.symbolClass = symbolsList.ElementAtOrDefault(i);
                        Calculations copy = calc;
                        test.ratingClass = performCalculations(test.symbolClass, copy, test.date); // passing a copy into the method for altering
                        stuffList.Add(test); // inserted a breakpoint here and the original class (calc) has been altered
                    }

Upvotes: 0

Views: 116

Answers (3)

Ian R. O&#39;Brien
Ian R. O&#39;Brien

Reputation: 6920

Let's walk through your code so you understand what is happening here. (What you are telling your code to do is written in the comments.)

// 1. create a new instance of the object 'Calculations' on the heap
// 2. return the memory address of that instance and assign it to variable 'calc'
Calculations calc = new Calculations(Symbol, Market);

// 3. Create a variable called 'copy' that points to 'Calculations' type objects
// 4. Assign the value of 'calc' (which is a reference to the heap object) to 'copy'
Calculations copy = calc;

Simply put, in your code calc and copy are pointing to the same object in memory. That is why changes to copy are affecting calc. What you need to do is clone your object so that you have a new object that is equal in value but separate in memory.

Upvotes: 3

Dai
Dai

Reputation: 155608

This code does not create a copy:

Calculations copy = calc;

In C# objects all exist on the heap and are manipulated through references, compare to C++ where you can create objects on the stack and assignment is equal to a copy operation.

Instead, implement IClonable and provide your own copy operation.

Upvotes: 5

Philip Stuyck
Philip Stuyck

Reputation: 7467

Calculations copy = calc;

is not creating a copy of your original data it is a reference to the same data. You need to clone this data.

More info on how to clone can be found here :

Deep cloning objects

Upvotes: 3

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