Article #25926: Resolving linker errors when using TRegistry

Question

Why am I getting unresolved external errors in the function ChangeKey when trying to link a class derived from TRegistry? [Linker Error] Unresolved external '__fastcall Registry::TRegistry::ChangeKey(int, const System::AnsiString)' referenced from C:\PROGRAM FILES\BORLAND\CBUILDER5\LIB\RELEASE\VCLE50.LIB|_t_Regis

Answer

This problem is very similar to one documented on our site regarding TMetafileCanvas. It is caused by a bug in the VCLE50.lib library, a library that allows the VCL (Pascal) library to be used in C++. In Pascal, Handles are treated as integer (unsigned), and in C++, they are treated as void pointers. The linker error was is given because the library was looking for a void pointer and passing in an int, which is incompatible with the unsigned that is actually in the VCL. One work around is to edit the VCL header file Registry.hpp, changing the type of the first parameter of the ChangeKey function from 'HKEY' to 'unsigned int'. After this change, calling ChangeKey will require typecasting the first parameter to unsigned int. While this works, it is not the best solution. When the bug causing this problem is fixed, the typecast will no longer be necessary and will cause compiler errors when the source is recompiled. A much better fix is to change the actual library so that the bug no longer occurs. This is not normally a very wise course of action because it can actually corrupt core VCL libraries and severely harm C++Builder, but in this case, the fix has been tested and it works. To undo this bug, simply copy and paste the code below into notepad and name the file RegFix.asm. Then, in a command shell (DOS box), run the following: tasm32 /ml RegFix.asm <copy RegFix.obj into $(BCB)\lib\debug and $(BCB)\lib\release> tlib /C vcle50.lib +RegFix.obj (do in both \lib and \release) This will patch the library and the error will cease. .386 .MODEL FLAT .CODE EXTRN @Registry@TRegistry@ChangeKey$qqruix17System@AnsiString:NEAR _TEXT segment dword public 'CODE' use32 @Registry@TRegistry@ChangeKey$qqrix17System@AnsiString segment virtual @@Registry@TRegistry@ChangeKey$qqrix17System@AnsiString PROC jmp @Registry@TRegistry@ChangeKey$qqruix17System@AnsiString @@Registry@TRegistry@ChangeKey$qqrix17System@AnsiString ENDP @Registry@TRegistry@ChangeKey$qqrix17System@AnsiString ends _TEXT ends END

Last Modified: 26-SEP-00