VC, passing Array of Strings between a C/C++ DLL and VB

passing Array of Strings between a C/C++ DLL and VB

Author	Message
GregMil #1 / 4	passing Array of Strings between a C/C++ DLL and VB Hi I need to pass an array of strings between a DLL written in C/C++ and a calling language like VB or Powerbuilder. I would leave it to the calling routine to allocate the memory for the array. The "C" DLL routine would just fill it in and return to the calling function. What is the typical way of passing arrays of strings between VB and C/C++ DLL? I've seen some comments on SafeArray. thanks * Sent from RemarQ http://www.--.com/ The Internet's Discussion Network The fastest and easiest way to search and participate in Usenet - Free!
Fri, 30 Aug 2002 03:00:00 GMT

Larry Brasfiel #2 / 4	passing Array of Strings between a C/C++ DLL and VB Quote: > Hi Hi. > I need to pass an array of strings between a DLL written in > C/C++ and a calling language like VB or Powerbuilder. I would > leave it to the calling routine to allocate the memory for the > array. The "C" DLL routine would just fill it in and return to > the calling function. > What is the typical way of passing arrays of strings between VB > and C/C++ DLL? I've seen some comments on SafeArray. Arrays of anything are passed to/from VB with the SAFEARRAY struct. One of the fields in it siginfies the content type so it can be disposed of properly. Among the types supported is BSTR, which is VB's string type. You would do better to just allocate the BSTR's and the array yourself, in the called routine, rather than trying to get this done in VB. The code will be no more complicated, it will reside in the right place for efficiency and convenience, and it will be most consistent with the way VB normally works and is used. BTW, a SAFEARRAY of BSTR is the typical way. -- Larry Brasfield Above opinions may be mine alone.
Fri, 30 Aug 2002 03:00:00 GMT

GregMil #3 / 4	passing Array of Strings between a C/C++ DLL and VB Thanks for the response Larry. One more quick question - are you suggesting that I allocate the array within the C/C++ Dll? If so, then i would have to make sure to free up the memory with another call to the dll - correct? I just want to make sure that whatever method I use to solve this issue is one that is generally accepted. thanks Greg * Sent from RemarQ http://www.remarq.com The Internet's Discussion Network * The fastest and easiest way to search and participate in Usenet - Free!
Fri, 30 Aug 2002 03:00:00 GMT

Larry Brasfiel #4 / 4	passing Array of Strings between a C/C++ DLL and VB Quote: > Thanks for the response Larry. You're welcome. Quote: > One more quick question - are > you suggesting that I allocate the array within the C/C++ Dll? Yes. Quote: > If so, then i would have to make sure to free up the memory with > another call to the dll - correct? No. One of several advantages to doing it per my suggestion is that you are using the same protocol that VB itself uses. If you pass a SAFEARRAY *, (which is the equivalent of a ByRef array in VB), all allocation issues will be properly handled on the VB side as long as you do your part on the DLL side. That means, for example, that you free any array that comes in if you have to reform it. The array will be treated by VB just as one of its own because that's what it will be. This means it will be freed as appropriate. Quote: > I just want to make sure that whatever method I use to solve > this issue is one that is generally accepted. What I suggested is the* way accepted by VB and what it uses internally. Take a look at the routines SafeArrayCreate(), SafeArrayDestroy(), SysAllocString(), SysFreeString() and associated routines. Quote: > thanks Sure. -- Larry Brasfield Above opinions may be mine alone.
Fri, 30 Aug 2002 03:00:00 GMT

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