Why does VS think this statement is always true?

Question

I have this if statement -

if (!((main.property == 1)||(main.property == 2))) { ... } 

main.property is a byte that is 0, 1, 2, or 98.

Visual studios say this statement is always true, but I don’t understand why?

If the value 1 or 2 should not be false.

Thanks in advance.

Edit: code added

file1.cs

 private void Upload(DataSet ds) { Main main = CreateMain(ds); //This is tested and works correctly if(ValidateDate(main)) { ... } } 

file2.cs

 internal static bool ValidateData(Main main, ...) { if (!((main.property == 1)||(main.property == 2))) { ... } } 

Edit: code added

If I do this, the error will disappear -

 internal static bool ValidateData(Main main, ...) { main.property = 0; //Or = any number if (!((main.property == 1)||(main.property == 2))) { ... } } 

I assume that VS thinks it is not initialized, but I am 100% sure of that.

Answer 1

I wrote this little program to check it out:

  class Program { static void Main(string[] args) { test(0); test(1); test(2); test(3); Console.ReadLine(); } private static void test(int p) { bool b1 = (!((p == 1) || (p == 2))); bool b2 = (p != 1 && p != 2); Console.Out.WriteLine("{0} {1} {2}", b1, b2, b1 == b2); } } 

It seems that Konstantin is right in his transcription, but not one expression is always true or always false.

Answer 2

Pre-PS: Inspired by Jon Skeet's comment above, I suggest you do the following:

• (Optional: back up the current code.)
• Simplify your code by gradually removing parts of it until the warning disappears. *
• As soon as the warning disappears, you will find out which parts of your code caused the error (namely, the part that you deleted last), and then you can understand it.

( Where did this advice come from? → You already saw that you can make the warning go away by adding code. I think your understanding of the problem will be even better when you do the opposite, that is, delete the code to get to the bottom of the problem.)

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main.property can only have values ​​0, 1, 2, and 98, and you said that your code ( CreateMain ) works correctly in this regard.

Thus, I assume that VS assumes that main.property will always be 0. Why this should come to this conclusion, I do not know. Perhaps he thinks he was not initialized.

I wrote code similar to yours and I don’t get this warning - I don’t even get a warning when I declare main.property as readonly and initialize it to 0. Thus, you probably main.property up in one of these situations when the crash code analysis / debugger VS.

Possible (though unlikely) reasons:

• Is there any code path where main.property not initialized?

• Since main.property is of type byte (at your discretion), maybe the warning is somehow caused by an overflow or overflow? (What happens if you change the type to int ?)

• Could it be that main obscures another main variable?

Answer 3

Go through your code to find out what the value of main.property is.

I had a similar problem, and that was because the value was null by default.

Answer 4

Since you are claiming that main.property is a byte that is 0, 1, 2, or 98, you should state this condition at the beginning of this method as such:

 internal static bool ValidateData(Main main, ...) { System.Diagnostics.Debug.Assert(main.property == 0 || main.property == 1 || main.property ==2 || main.property == 98); if (!((main.property == 1)||(main.property == 2))) { ... } }