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Create DLL using Turbo C ?

How can I create DLL for my Visual Basic Application using turbo C?
anikAsked:
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mlaiosaCommented:
what version of turbo C, of VB
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anikAuthor Commented:
turbo C++ 3.0, Visual Basic 6.0
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prozakCommented:
I haven't actually done this with TC but I can tell you how to do it with MS VC++. All of you functions must be declared with the extern "C" qualifier if you're using C++ to prevent name mangling. Additionally all the functions that will be called by you VB program must be declared as stdcall (This affects how arguments are passed to function). And finally when compiling the DLL (this is under VC++ only as far as I know) I had to define a .def (module definition) file and specifically export each function in that, otherwise when I called the function from VB I would get an error "Could not find entry point" or something like that. Also when you declare the function in VB if it's ByVal then you just get the value (i.e. ByVal myVar As Long would be long myvar in C and ByRef myVar as Long would be long *myvar in C. After reading this last sentence, I guess you could've figured that one out by yourself :) Strings must be passed as ByVal so VB can do the translation from a multi-byte string (16-bit characters) to a byte string (8-bit ASCII characters). The only way I've found to get access to the multi-byte versions of VB strings is if the value is passed as type Variant. If you try to pass the string as ByRef, you get a pointer to a pointer to the string but VB still packs all the characters to 8-bits. All of this info is for VB5. I haven't used VB6 yet but I've heard that in this respect it is the same.
Hope this helps!
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peterpan1975Commented:
there (at VStudio vb cd) is a file vb5dll.doc:
\vb5.0\tools\docs
very good explanation how to connect VC 4.0 dll's to vb... Im not sure if it applies to TC, but I hope it might be helpful as well :)
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