Why short(-1) not equal to -1 in c#

Question

In MVC4,.net 4.6.1 and VS 2015, I write a simple MVC app to pass a short type value from view to controller like this

public bool GetTheValue (short req_division)
{ return req_division == -1 ;}

The weird thing is when I pass -1 to req_division from my view, the result returned false. I don't know why is it happened. Can anyone explain it for me. Thank you very much !

What is the difference between `value` and `val`? And why do both exist? — Farhad Jabiyev, Oct 31 '16 at 10:10
And, as an aside, based on the versions you mentioned, you have the following syntax available: `bool GetTheValue (short val) => val == -1;` — , Oct 31 '16 at 10:12
@TranQ post your *actual* code. What's bothering people is having to guess — Panagiotis Kanavos, Oct 31 '16 at 10:18

score 12 · Accepted Answer · answered Oct 31 '16 at 10:13

12

Besides the possible typo in your code, I found something strange in the evaluation that the Debug View does. See this code:

The debugger says it is false, yet the code evaluates to true. Maybe you have hit a type conversion issue in the debugger. When changing the int to a short, the debugger thinks i == j evaluates to true after all.

answered Oct 31 '16 at 10:13

Patrick Hofman

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There is no `Equals` used here @JᴀʏMᴇᴇ, so it doesn't apply here. And clearly the debugger is bad here since it doesn't evaluate the way the code does. – Patrick Hofman Oct 31 '16 at 10:17
Excellent answers on that other post by the way ;) – Patrick Hofman Oct 31 '16 at 10:19
`-1` is an integer literal. The debug viewer probably doesn't perform the implicit cast, which I suspect is language-specific behaviour – Panagiotis Kanavos Oct 31 '16 at 10:20
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That means that the debugger doesn't actually run the code the way the CLR / compiler does, which we already knew @Pan :) – Patrick Hofman Oct 31 '16 at 10:21
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@JᴀʏMᴇᴇ On the question you linked: http://stackoverflow.com/a/33362835/993547 :) – Patrick Hofman Oct 31 '16 at 10:23
The debugger in this case evaluates a debugger expression, not actual code. It does look strange though debugging in C# doesn't use the C# conversion rules. – Panagiotis Kanavos Oct 31 '16 at 10:23
@PatrickHofman - haha I'd totally missed that. Right, let me have this coffee and start the day over again. Slow start so far. – Oct 31 '16 at 10:27

Why short(-1) not equal to -1 in c#

1 Answers1