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Virtual Declaration

Started by phyl0men0 Jan 14, 2003 at 2:40 PM 1 reply 750+ views

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Jan 14, 2003 at 2:40 PM

Hi all I have 2 projects, an executable and a DLL. Executable: In this project I have a class called classA, which is declared in a normal header file. There are a few member functions. The definitions of this functions are in a normal cpp file. DLL This DLL only includes the header file of classA(from the executable). The DLL receives an pointer to an classA and tries to call a member function of classA. When I try to compile I receive a linker error "unresolved symbols...". But when I declare all the functions in the classA as virtual all works fine. Can somebody explain that to me? thx phyl0men0

Jan 14, 2003 at 5:37 PM

in the dll, the addresses of the member functions are unknown so it can''t call them; if the function is virtual, the class instance to which you get a pointer in the dll has got a vtable (or a pointer to a vtable), in the vtable the addresses of the virtual functions are stored, so the virtual functions can be called without knowing the addresses of their implementations.

phyl0men0

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