Delphi: EInvalidOp exception, might just mean you have a use-after free scenario, or an out-of-bounds value
Posted by jpluimers on 2021/05/13
Quite some time ago, I was researching spurious exceptions in a Delphi application, then finally replicated them in a unit test suite.
One of them was occurring almost all of the time: EInvalidOp.
It is one of the floating point exceptions (incidentally exampled at [WayBack] Exceptions: Declaring Exception Types) all inheriting from the [WayBack] EMathError Class:
EMathErroris the base class for floating-point math exception classes.EMathErroritself is never raised.The following exceptions descend from
EMathError:
Run-time exception information is saved in fields provided by [WayBack]
EExternal.
Use-after-free
In my first case (which I described in delphi – Invalid floating point operation calling Trunc()), not all input scenarios had been tested in a certain scenario. In a production environment, one of the inputs was really high.
In a later case, the actual cause was not a floating point problem at all, but a use-after-free scenario that overwrite a floating point value with something not so compatible also causing a simple Trunc statement to fail in the same way.
In that case, the production data could never reach the big numbers that failed, so no new tests were needed.
–jeroen
The Wiert Corner - irregular stream of stuff 
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