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VB Forum / COM / February 2005How to convert LPCByte and LPByte into a VB Data Type
Hi Guys, I need to use winscard.dll and hence am declaring the functions that i need. However, i got stuck in trying to find suitable VB Data types for LPByte and LPCByte used in SCardTransmit. Any help rendered very much appreciated. > Hi Guys, I need to use winscard.dll and hence am declaring the functions that > i need. However, i got stuck in trying to find suitable VB Data types for > LPByte and LPCByte used in SCardTransmit. Any help rendered very much > appreciated. Are you using COM? Or creating an API (functions exported as _stdcall/winapi)? What have you tried so far? What errors/problems are you having? VB to C? C to VB? VB has a Byte type (unsigned char) which can be passed ByRef, a pointer to type. -ralph Hi Ralph. Well i'm declaring the winscard.DLL procedure in my VB project so i guess that makes it C to VB. I was looking through MSDN's converting C declarations to VB (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon98/html/vb condeclaringdllprocedure.asp) but it didnt state the declarations i should use for the two data types LCByte and LPByte. Any help in clearing this one up will really be appreciated. Thx > > Hi Guys, I need to use winscard.dll and hence am declaring the functions > that [quoted text clipped - 11 lines] > > -ralph > Hi Ralph. Well i'm declaring the winscard.DLL procedure in my VB project so > i guess that makes it C to VB. I was looking through MSDN's converting C > declarations to VB (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon98/ht ml/vbcondeclaringdllprocedure.asp) > but it didnt state the declarations i should use for the two data types > LCByte and LPByte. Any help in clearing this one up will really be > appreciated. > > Thx Use "ByRef lpByte As Byte > Hi Ralph. Well i'm declaring the winscard.DLL procedure in my VB project so > i guess that makes it C to VB. I was looking through MSDN's converting C > declarations to VB (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon98/ht ml/vbcondeclaringdllprocedure.asp) > but it didnt state the declarations i should use for the two data types > LCByte and LPByte. Any help in clearing this one up will really be > appreciated. > > Thx I don't have access to wincard at the moment so I can't see the signatures, but try ByRef lpByte As Byte ' Byte is an 8-bit number ByRef lpcByte As Byte "Constantance" is a concept only known to C, so lpc and lp are the same to VB. "ByRef" is the default. All VB variables are 'references' by default. So ByRef passes a pointer to a 'container'. ByVal would pass the 'value'. So by committing a bit of heresy... A C signature of "unsigned char* lpByte;" is a VB signature of "ByRef lpByte As Byte". A C signature of "char cByte;" is a VB signature of "ByVal cByte As Byte". Note: VB only truly understands the parameter attributes of [in] and [in, out]. (Well, also [in, retval], but that's another story.) It doesn't understand [out] by value very well at all, but always gives it a good old try. If you don't mind ugly, you can always use ... ByRef lpByte As Any and in VB use... SomeVar = CByte(lpByte) <g> hth -ralph |
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