16/32 Bit Strings

16/32 Bit Strings

Is there a difference in the way that strings are passed between an application written in Delphi 1.0 and a DLL and between an application written in Delphi 3.0 and a DLL? For example, are the strings in Delphi 3.0 null terminated?

Yes, there is a definite difference between strings in Delphi 1.0 and Delphi 3.0. Delphi 1.0 strings are traditionally ShortStrings–nothing more than character arrays of 256 bytes. Delphi 2.0 (and later versions) strings are AnsiStrings, which are actually pointers to null-terminated strings. Furthermore, AnsiStrings have a negative offset that contains the “length code” as opposed to ShortStrings that have a zero-offset that contains the “length byte.” What does this mean? Well, the length code of an AnsiString is a 32-bit code, which means that it can be as large as 4GB. AnsiStrings in Win32 can be as large as that. On the other hand, since the length byte of a ShortString is only 8-bits, the largest value it can be is 256. So there are fundamental differences between strings in version 1 and 2+. Based on what I explained above, the Delphi 3.0 string is not really null-terminated. However, the data that the string pointer variable points to is null-terminated. So to answer your question, strings passed in an application written in the different versions of Delphi are handled differently by virtue of their very different natures.


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