BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  SubClassing VirtualTreeView          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Usage) View previous topic :: View next topic   Author Message masi Guest Posted: Mon Feb 27, 2006 3:03 pm    Post subject: SubClassing VirtualTreeView A question about using Virtual TreeView with BCB6 or BCB2006: If I try to subclass TVirtualStringTree I get the following error: [Linker Error] Unresolved external '__fastcall Virtualtrees::TBaseVirtualTree::DoGetHeaderCursor(void *&)' referenced from MyVirtualStringTree.obj No problem if I put a TVirtualStringTree object on a form, but what I'd like is to have a component which is a subclass of TVirtualStringTree. What's wrong? thanks masi urbano Back to top masi Guest Posted: Mon Feb 27, 2006 6:03 pm    Post subject: Re: SubClassing VirtualTreeView Quote: To get terms correct "subclassing" means you take control of a windowed control's message handling function and process certain messages before the class can. What you are doing is descending a class from TVirtualStringTree. Yes, I wanted to mean that. Thanks. Quote: The problem you are encountering is a BCB compiler bug that does not create the correct mangled function name compared to what the Delphi compiler does. I thought Borland had fixed this for BDS but apparently they have not. Add the following line to your C++ code (note, this is all one line). #pragma alias "@Virtualtrees@TBaseVirtualTree@DoGetHeaderCursor$qqrrpv" = "@Virtualtrees@TBaseVirtualTree@DoGetHeaderCursor$qqrrui" Many thanks again masi urbano Back to top Clayton Arends Guest Posted: Mon Feb 27, 2006 6:03 pm    Post subject: Re: SubClassing VirtualTreeView "masi" <masiurb (AT) tin (DOT) it> wrote in message news:440308b6$1 (AT) newsgroups (DOT) borland.com... Quote: If I try to subclass TVirtualStringTree I get the following error: To get terms correct "subclassing" means you take control of a windowed control's message handling function and process certain messages before the class can. What you are doing is descending a class from TVirtualStringTree. The problem you are encountering is a BCB compiler bug that does not create the correct mangled function name compared to what the Delphi compiler does. I thought Borland had fixed this for BDS but apparently they have not. Add the following line to your C++ code (note, this is all one line). #pragma alias "@Virtualtrees@TBaseVirtualTree@DoGetHeaderCursor$qqrrpv" = "@Virtualtrees@TBaseVirtualTree@DoGetHeaderCursor$qqrrui" HTH, - Clayton Back to top masi Guest Posted: Mon Feb 27, 2006 11:03 pm    Post subject: Re: SubClassing VirtualTreeView Quote: Add the following line to your C++ code (note, this is all one line). #pragma alias "@Virtualtrees@TBaseVirtualTree@DoGetHeaderCursor$qqrrpv" = "@Virtualtrees@TBaseVirtualTree@DoGetHeaderCursor$qqrrui" Ok, it works fine on bcb6 But on BCB2006 I still got: [Linker Error] Error: Unresolved external '__fastcall Virtualtrees::TBaseVirtualTree::OriginalWMNCPaint(void *)' referenced from ......MYVIRTUALTREE.OBJ any idea? Back to top Clayton Arends Guest Posted: Tue Feb 28, 2006 8:03 pm    Post subject: Re: SubClassing VirtualTreeView Apparently I had "fixed" this problem before by simply removing the virtual from the declaration since it was never used as a virtual anywhere. The real fix is to use the same #prama line but replace DoGetHeaderCursor with OriginalWMNCPaint. The mangling should be the same (I will check on that later if it doesn't work for you). - Clayton Back to top masi Guest Posted: Wed Mar 01, 2006 8:03 am    Post subject: Re: SubClassing VirtualTreeView Quote: Apparently I had "fixed" this problem before by simply removing the virtual from the declaration since it was never used as a virtual anywhere. Which declaration? Quote: The real fix is to use the same #prama line but replace DoGetHeaderCursor with OriginalWMNCPaint. The mangling should be the same (I will check on that later if it doesn't work for you). No, it doesn't work with BCB2006: I got the same error [Linker Error] Error: Unresolved external '__fastcall Virtualtrees::TBaseVirtualTree::OriginalWMNCPaint(void *)' referenced from ......MYVIRTUALTREE.OBJ many thanks for your help. masi urbano Back to top Clayton Arends Guest Posted: Wed Mar 01, 2006 10:03 pm    Post subject: Re: SubClassing VirtualTreeView "masi" <masiurb (AT) tin (DOT) it> wrote in message news:4405483a$1 (AT) newsgroups (DOT) borland.com... Quote: Which declaration? In VirtualTrees.pas: procedure OriginalWMNCPaint(DC: HDC); virtual; All I had done long ago was to remove the virtual. This wasn't really the best solution since it requires a source change. It's of no consequence though since the correct solution is below. Quote: No, it doesn't work with BCB2006: I got the same error Try this: #pragma alias "@Virtualtrees@TBaseVirtualTree@OriginalWMNCPaint$qqrpv" = "@Virtualtrees@TBaseVirtualTree@OriginalWMNCPaint$qqrui" Again, this is all on one line. - Clayton Back to top masi Guest Posted: Thu Mar 02, 2006 10:03 am    Post subject: Re: SubClassing VirtualTreeView Quote: Try this: #pragma alias "@Virtualtrees@TBaseVirtualTree@OriginalWMNCPaint$qqrpv" = "@Virtualtrees@TBaseVirtualTree@OriginalWMNCPaint$qqrui" it's magic for me, but it works fine! thanks you very much masi urbano Back to top Clayton Arends Guest Posted: Thu Mar 02, 2006 11:03 pm    Post subject: Re: SubClassing VirtualTreeView "masi" <masiurb (AT) tin (DOT) it> wrote in message news:4406b803$1 (AT) newsgroups (DOT) borland.com... Quote: it's magic for me, but it works fine! It does appear that way at first. Here is a breakdown (though probably not entirely accurate since I don't know all of the inner workings of the compiler/linker). Compilers that support classes and same-name functions must create a name mangled function name to tell two functions apart from one another. They do this by taking the names of the parameters in the function and tacking them in some obscure format to the end of the function name. In practice though the compiler can make any name it wants as long as the same name is always created for a particular reference. Here is an example of how BCB and Delphi do things. TVirtualStringTree exists in the "Virtualtrees" namespace. Here is the fully qualified name of the method: // C++ Virtualtrees::TVirtualStringTree::OriginalWMNCPaint(HDC) // Object Pascal (Delphi) Virtualtrees.TVirtualStringTree.OriginalWMNCPaint(HDC) The problem stems from how the two compilers mangle names. Delphi treats the HDC type (and all other Windows handles) as "unsigned integer" while BCB treats the HDC type as "pointer to void". Following is the name mangled version of the above method: // C++ @Virtualtrees@TVirtualStringTree@OriginalWMNCPaint$qqrpv // Delphi @Virtualtrees@TVirtualStringTree@OriginalWMNCPaint$qqrui Notice the difference "pv" (pointer to void) and "ui" (unsigned integer). "#pragma alias" tells the compiler that any references to the name on the left should really look like the name on the right. So, given the pragma that I gave you before it converts all references to the C++ mangled name to the real mangled name compiled by Delphi. One way to know the mangled name would be to memorize it. However, I have precious space left in my brain so I choose to determine the mangled name using tools at my disposal. First I find the function that the C++ linker cannot find in the PAS source. I then lookup that function name in the corresponding BPL using Dependency Walker. If I can't find the BPL I create a dummy PAS file and recreate the function. Then I make a C++ version of the function and export it using the PACKAGE keyword in some test project. I compile into an EXE and look up the mangled name using DW. Once I know the two mangled names I can then make the #pragma. It is very rare that I have to do this but it is a good trick to know when the problem crops up. - Clayton Back to top masi Guest Posted: Fri Mar 03, 2006 1:57 pm    Post subject: Re: SubClassing VirtualTreeView Quote: // C++ Virtualtrees::TVirtualStringTree::OriginalWMNCPaint(HDC) // Object Pascal (Delphi) Virtualtrees.TVirtualStringTree.OriginalWMNCPaint(HDC) The problem stems from how the two compilers mangle names. Delphi treats the HDC type (and all other Windows handles) as "unsigned integer" while BCB treats the HDC type as "pointer to void". Following is the name mangled version of the above method: // C++ @Virtualtrees@TVirtualStringTree@OriginalWMNCPaint$qqrpv // Delphi @Virtualtrees@TVirtualStringTree@OriginalWMNCPaint$qqrui Notice the difference "pv" (pointer to void) and "ui" (unsigned integer). "#pragma alias" tells the compiler that any references to the name on the left should really look like the name on the right. It is very rare ... But it happens sistematically everytime a virtual function has HDC, CURSOR, etc. parameters, doesn't it? Many thanks for your help and I appreciated much your explanation. masi urbano Back to top Clayton Arends Guest Posted: Fri Mar 03, 2006 6:03 pm    Post subject: Re: SubClassing VirtualTreeView Perhaps "very rare" isn't a correct assessment <g>. It happens more often for component writing than it does for application development. But anyhow, I'm glad the information was useful to you. 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