Re: Casting double to int produces inconsistent results from VS 2003 to VS 2008

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.language
Date:
Sat, 28 Mar 2009 10:57:40 -0400
Message-ID:
<##lEPW7rJHA.3992@TK2MSFTNGP04.phx.gbl>
"KD" <keith.degrace@gmail.com> wrote in message
news:44295413-bcab-40a8-bfdf-9627c505d7b6@w34g2000yqm.googlegroups.com

I am porting some legacy code from VS 2003 to VS 2008, and I've
encountered a problem. Here is an example to illustrate:

{
   double f = 10000000000.0;

   int d = (int) (f);
}

When I run from VS2003, I get:
d = 1410065408

When I run from VS2008, I get:
d = -2147483648

Can someone please explain why d2 is different in VS 2008?


I can't explain why, but I can explain the numbers. 10000000000 is
0x2540BE400. Truncated to 32 bit, it becomes 0x540BE400, or 1410065408
in decimal. You'll likely get the same result on VS 2008 (and also on VS
2003) with

int d = (int) (long long) (f);

-2147483648 is 0x80000000, or INT_MIN. Not quite clear why this value,
and not INT_MAX, was chosen to represent integer overflow.
--
With best wishes,
    Igor Tandetnik

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