Problems with short and + operator

  • Thread starter Thread starter NilsNilsson
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NilsNilsson

I wrote this:
short s1 = 0;
short s2 = 1;
short s3 = s1 + s2;

And gor this compile error message: Cannot implicitly convert type 'int' to
'short'

What is wrong here?

Regards
Anders
 
NilsNilsson said:
I wrote this:
short s1 = 0;
short s2 = 1;
short s3 = s1 + s2;

And gor this compile error message: Cannot implicitly convert type 'int' to
'short'

What is wrong here?
Click to expand...

Any operation involving two shorts has a type of int. In other words,
you need:

short s3 = (short) (s1+s2);
 
Thus spake NilsNilsson:
Thanks,
it works!

But I still think this is strange feature i C#?
Click to expand...

It's a safeguard against overflow errors. Your operation may produce a
result that exceeds the storage capacity of the short data type.

BTW, the help on the short data type actually states that your original
code will produce an error.
 
This is not really specific to C#, you will get the same thing in Java.

Bruno.

NilsNilsson said:
Thanks,
it works!

But I still think this is strange feature i C#?

/Anders

'int'
Click to expand...
 
The reason this is the case is because the CLR evaluation stack uses 4-byte
and 8-byte integers, so the short will get widened when it is pushed on the
stack, and then the add instruction comes up with an Int32 result.

The compiler could generate code to automatically cast this back to short
for you, however this would be hiding some of the details of what was
actually going on, would be limiting functionality, and would be prone to
errors. Consider the following method:

public void Method()
{
checked {
short a = 0x7fff;
short b = 0x7fff;
int c = a + b;
}
}

The method will work with the current system. Suppose, however, that the
compiler forced a cast back to short behind the scenes. Then the last line
would change to something like:

int c = (int)(short)(a + b); // where the cast to short is added by
the hypothetical compiler

Not only would you get an invalid result due to overflow errors on the cast
to short, but in this case it would always throw an exception because it is
in a checked context.

-Mark

--
Mark Andersen, Visual C# Team
This posting is provided "AS IS" with no warranties, and confers no rights.
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--------------------
From: "NilsNilsson" <[email protected]>
References: <[email protected]>
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Subject: Re: Problems with short and + operator
Date: Wed, 24 Sep 2003 10:17:56 +0200
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Thanks,
it works!

But I still think this is strange feature i C#?

/Anders

'int'
Click to expand...
 
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