Why does including FastMM cause an EInvalidTypecast error?

Question

This is with Delphi XE2 and FastMM 4.99, and a 32-bit program on a Win7-64 machine.

I was trying to use FastMM to check a smallish program I've been working on. The program includes a data module that is on the project's auto-created forms list. The data module contains only a TADOConnection object.

When I enable FullDebugMode in FastMM, I get an invalid typecast error when exiting the program. The culprit seems to be in freeing the datamodule (the error occurs in TADOConnection.GetADODataSet). Can anyone suggest why this is happening?

Clearly it's happening because the code attempts a typecast that is invalid. Without being able to see the code it's pretty hard to be more specific. If you want help, provide adequate details. — David Heffernan, Sep 20 '12 at 18:54
Install MadExcept and at least you'll find out WHERE the error is happening. — Warren P, Sep 20 '12 at 19:13

score 3 · Accepted Answer · answered Sep 20 '12 at 21:19

3

It turns out that the problem was just something that was exposed by FastMM, not caused by it.

Specifically, I'd subclassed TADOQuery for use with the data module. I remembered to write a destructor override for the class, but failed to call the inherited dtor. Probably this was causing the TADOConnection to do something undefined.

answered Sep 20 '12 at 21:19

wades

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Didn't that give you a COMPILER WARNING? :-) – Warren P Sep 21 '12 at 21:42

score 0 · Answer 2 · answered Sep 20 '12 at 18:18

Without more information, it's hard to say exactly, but when you're having problems when freeing something, it's usually because it's trying to free something that's already been freed. Try placing a few breakpoints to see if any of the classes involved are getting freed before you see this error. If so, that should help you track it down.

Why does including FastMM cause an EInvalidTypecast error?

2 Answers2