[fpc-devel] Access Violation withnested DLL'scompiledbyFPC(andsome more info on bug #4538)

L505 fpc505 at z505.com
Thu Dec 15 05:45:45 CET 2005

> In short (don't pin me on the names or on exact details in special cases):
> Assume you have a ansistring and you assign something to it
>    S := 'SomeString';
> the compiler generates something like
>    DecStringRef(S);
>    S -> 'SomeString';
>    IncStringRef(S);
> The DecStringRef() decrements the refcount and checks if the it reaches
> zero. Ifso, the string is freed. The referencecounter of a strings lies

Why does it generate a DecStringRef before you assigned the string? What if it is the
first time and you are already at 0, it can't decrement it to -1 can it?
Does the reference count start at 0, or 1?

In this case, it decrements 1 and increments 1, so we will always end up with a very
simple, easy, solvable problem.

1 - 1 = 0
1 - 1 = 0

That seems like it isn't doing anything useful, since we are incrementing and
decrementing by one, every time we assign a string.

What Jonas said was that the reference count would be 1 (one) when you pass it to a
DLL. You are saying it will be 0 (zero). We have two people saying opposite things
here, so I'm really not sure what is going on. What would be logical to me, is if the
reference count was 1, not zero.

I guess when I finally understand this science, I will write a diagram showing how it
works in a Pascal procedure or function with comments beside each code snippet saying
what the reference count is.

If there is a PDF file that explains this or some good website let me know. I hate to
embarrass myself here (maybe other people are confused too, though).


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