'static' value appears to reset after function call

EmerG Published at

EmerG :

I found a lot of articles about statics (MSDN, MSDN 2, Stack Overflow, and lot lot more), but I still can't understand why this code returns -1:

class Program
{
    static int value = 0;

    static int foo()
    {
        value = value - 7;
        return 1;
    }

    static void Main(string[] args)
    {
        value -= foo();
        Console.WriteLine(value);
        Console.ReadKey();
    }
}

Here's what the debugger shows after foo() has run, but before the result is subtracted from value:

But one step later, value is -1:

I would expect -8 because of the static field which is stored in memory once.

When I changed it to

var x = foo();
value -= x;

it shows -8

How does this work exactly?

shingo :

This problem is not about static; it's about how the subtraction works.

value -= foo(); can be expanded to value = value - foo()

The compiler will explain it into four steps:

Load the value of value onto the stack.
Call the method foo and put the result onto the stack.
Do subtraction with these two values on the stack.
Set the result back to value field.

So the original value of value field is already loaded. Whatever you change value in the method foo, the result of the subtraction won't be affected.

If you change the order to value = - foo() + value, then the value of value field will be loaded after foo is called. The result is -8; that's what you are expected to get.

Thanks for Eliahu's comment.

Collected from the Internet

Please contact [email protected] to delete if infringement.

edited at2020-09-13

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