Re: C++Builder and Delphi Exceptions

Mihai,

> I am doing a research project in C++Builder 5.0 and
> I'm using large numbers.
>
> I have some problems with exception handling.
>
> If I perform some operations that overflow the
> capacity of the double data type I usually get an
> EOverflow exception.
>
> But, sometimes the variables that stores the results
> are filled with some C++Builder constants (such as NAN
> or INF) and no exception is thrown. But, if I use
> these
> variables (filled with NAN or INF) I get an error and
> my application stops.
>
> My question is how could I handle all these exception
> in a uniform manner? I wrote several test functions
> that check whether the variables contain the NAN and
> INF constants, but this significantly slows down my
> application. So I don't want to use this functions
> anymore, but I need some mechanisms for preventing
> such situations.

My experience is with Delphi, not BCB, but I can give you a few thoughts.

First, an overflow of the Double type may not result in an EOverflow
exception.  If the FPU/NPU has encountered an underflow or denormal since it
was last reset, Delphi gives an EInvalidOp instead of EOverflow.  (I don't
know what BCB does.)  I suggest you test for EMathError instead, since this
catches all overflow exceptions.

You should determine just how those NANs and INFs are getting into your
data.  They do not easily result from normal operations.  I believe that the
most common ways they result are from the FPU control word changed to ignore
overflow and other errors, constants (which means *you* put them in your
program), or from floating fields in a database.  You could probably save
time by checking these special values only at input (and ensuring the FPU
control word is not changed).

How complicated is your test for INF/NAN?  If you don't need to distinguish
between them, there is a simple test for "special" values for a double
variable:

  if (Int64(DblVariable) and $7FF00000) = $7FF00000 then ...

HTH.

Rory Daulton
[email protected]
Campus Crusade for Christ


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