[DUG] Delphi Calling Convetion is Weird!!

[Rohit Gupta]

Stacey,

They broke this in D3.  I had to rewrite a lot of my old Borland Pascal 
code at that time.   Borland also made a statement that the order of 
evaluation is not defined in the language and should not be relied on.  
It has nothing to do with the calling convention.

Its a pain only for string manipulation.  :-)

Stacey Verner wrote:
>
> After an odd bug and a bit of testing I have found that the parameters 
> in Delphi (tested 6 and 2006) are evaluated very strangely.
>
>  
>
> The 3^rd parameter is evaluated first followed by 4, 5, 6 etc and then 
> the 2^nd and then the 1^st .
>
>  
>
> This appears to be because the default calling convention is 
> *register* which (from the documentation) puts up to 3 parameters in 
> registers and the rest on the stack. It seems to process the stack 
> ones first from parameters 3 onwards (Why 3? Shouldn't it be 4 if we 
> are putting 3 into registers. Must be only putting 2 in the 
> registers), and then the first 2 in reverse order into the registers. 
> The documentation also says that is supposed to pass the from left to 
> right, but it obviously doesn't.
>
>  
>
> You can download an example to see for yourself!
>
>  
>
> http://www.verner.co.nz/download/FunctionCall.zip
>
>  
>
> If you are interested how we found this, we have a simple function 
> that strips the first delimited item from a string returning the item 
> and removing it from the input string. You can have a string something 
> like:
>
>  
>
> LString := 'Stacey,G,Verner';
>
>  
>
> and call:
>
>  
>
> LFirstName := Extract(LString, ',');
>
> LInitial := Extract(LString, ',');
>
> LLastName := Extract(LString, ',');
>
>  
>
> In this case if we had a function like:
>
>  
>
> function FullName(PFirstName, PInitial, PLastName: String): String;
>
>  
>
> and you call it with:
>
>  
>
> LName := FullName(Extract(LString, ','), Extract(LString, ','), 
> Extract(LString, ','));
>
>  
>
> then we'll get the wrong result.
>
>  
>
> Stacey
>
>  
>
> Stacey Verner             Ph:   +64-9-4154790
> Software Developer        Fax:  +64-9-4154791
>                           DDI:  +64-9-4154797
>                           Email: stacey at cjntech.co.nz 
> <BLOCKED::mailto:stacey at cjntech.co.nz>
>
> CJN Technologies Ltd.
>
> PO Box 302-278, North Harbour, Auckland 1330, New Zealand
> 12 Piermark Drive, North Harbour, Auckland, New Zealand
> Visit our website at http://www.cjntech.co.nz/ 
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>
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-- 
*Rohit Gupta*
* B.E. Elec.   M.E.   Mem IEEE    Associate IEE*
*Technical Manager*
*Computer Fanatics Limited*
** 
*Tel*     +64 9 4892280
*Fax*    +64 9 4892290
*Email  *rohit at cfl.co.nz <mailto:rohit at cfl.co.nz>**
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