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    <p>The internal structure of AnsiStrings changed between Delphi 2007 and Delphi 2009. (Don't get upset; that possibility has been present since day 1.) A Delphi 2009 string maintains a number indicating what code page its data is in.</p> <p>I recommend you do what every other DLL on Earth does and pass character buffers that the function can fill. The caller should pass a buffer pointer and a number indicating the size of the buffer. (Make sure you're clear about whether you're measuring the size in bytes or characters.) The DLL function fills the buffer, writing no more than the given size, counting the terminating null character.</p> <p>If the caller doesn't know how many bytes the buffer should be, then you have two options:</p> <ul> <li><p>Make the DLL behave specially when the input buffer pointer is null. In that case, have it return the required size so that the caller can allocate that much space and call the function a second time.</p></li> <li><p>Have the DLL allocate space for itself, with a predetermined method available for the caller to free the buffer later. The DLL can either export a function for freeing buffers that it has allocated, or you can specify some mutually available API function for the caller to use, such as <code>GlobalFree</code>. Your DLL must use the corresponding allocation API, such as <code>GlobalAlloc</code>. (Don't use Delphi's built-in memory-allocation functions like <code>GetMem</code> or <code>New</code>; there's no guarantee that the caller's memory manager will know how to call <code>Free</code> or <code>Dispose</code>, even if it's written in the same language, even if it's written with the same Delphi version.)</p></li> </ul> <p>Besides, it's selfish to write a DLL that can only be used by a single language. Write your DLLs in the same style as the Windows API, and you can't go wrong.</p>
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    1. POAnsiString return values from a Delphi 2007 DLL in a Delphi 2009 application
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    1. USRob Kennedy
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    1. COIt's good to know that 2009 changed the ansistring definition, but rewriting DLLs makes the port to 2009 all the more onerous, and given the amount of code involved, will probably kill efforts to port to 2009 in our shop. Are there any other work arounds?
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    2. CO@Zartog: This has nothing to do with porting to Delphi 2009, and everything with having used improper data types in the DLL API. Trying to use the DLL from .NET or another language != Delphi would result in similar problems. Cleaning up the code base would be a good idea, even without a port to Delphi 2009. See "Technical Debt", for example http://martinfowler.com/bliki/TechnicalDebt.html
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