VB/WinAPI, VB calling C++ DLL returning an array??

VB calling C++ DLL returning an array??

Author	Message
Matt #1 / 4	VB calling C++ DLL returning an array?? Hello- I am having problems returing an array in a VB application when I a function in a c++ DLL. I get a referenced memory error. I know the DLL is being called correctly, but an error occurs at the point of returning the array. Here is a snipit of code from the VB and VC++ applications. Thanks in advance for any help! '*******************VB6.0 Code************************************************************* Dim RetArray() As Integer ReDim RetArray(intNumBytes) 'redim the array that is expected RetArray = ReturnArray(intNumBytes) 'call function in dll, return type=array of integers '*********************************************************************** ********************* //*****************VC++6.0 Code*********************************************************** int * Add::ReturnArray(int numberbytes) { int Value[100]; for(short int i=0;i<numberbytes;i++) { Value[i] = i; } return(Value); //************************************************************************ ************************ Best Regards, Matt Van Bergen
Mon, 21 Jan 2002 03:00:00 GMT

Jonathan Woo #2 / 4	VB calling C++ DLL returning an array?? I'm pretty sure this code won't compile in VB5. I haven't tested it too extensively with VB6. I guess there could be something new. But for starters, how can you call a C++ method from VB? I'd have thought the name mangling alone would be a major pain. Also, unless it is a static function, it needs the hidden "this" pointer to be passed, which VB obviously do. Beyond that, VB uses SAFEARRAYs for arrays. I have no idea how you declared the function you are calling but if VB is expecting it to return an array, it'd be expecting a SAFEARRAY and not just a pointer to an array of ints. Further, the DLL function declares the array on the stack and that data is invalid as soon as the function returns. It may work once or twice but you are asking for trouble here. If that's not enough, C++ ints are 32-bits and VB Integers are 16-bit so you also have a mismatch there. -- Jonathan Wood SoftCircuits Programming http://www.softcircuits.com Quote: > Hello- > I am having problems returing an array in a VB application when I a function > in a c++ DLL. I get a referenced memory error. I know the DLL is being > called correctly, but an error occurs at the point of returning the array. > Here is a snipit of code from the VB and VC++ applications. Thanks in > advance for any help! > '*******************VB6.0 > Code************************************************************* > Dim RetArray() As Integer > ReDim RetArray(intNumBytes) 'redim the array that is expected > RetArray = ReturnArray(intNumBytes) 'call function in dll, return > type=array of integers '*********************************************************************** - Hide quoted text - - Show quoted text - Quote: > ********************* > file://*****************VC++6.0 > Code*********************************************************** > int * Add::ReturnArray(int numberbytes) > { > int Value[100]; > for(short int i=0;i<numberbytes;i++) > { > Value[i] = i; > } > return(Value); file://******************************************************************* * - Hide quoted text - - Show quoted text - Quote: > ************************ > Best Regards, > Matt Van Bergen
Mon, 21 Jan 2002 03:00:00 GMT

Peter Beac #3 / 4	VB calling C++ DLL returning an array?? Matt, Try something like this: Private Sub MyArrExample lib "MyDLL.dll" (byval NumItems as Integer, ByRef RetArray As Integer) and use something like: Redim RetArr(14) as Integer MyArrExample 15, RetArr(0) The C++ end would be something like: extern "C" void WINAPI MyArrExample(short iNumItems, short lpsRetArray) { short i; for (i = 0; i < iNumItems; i++) lpsRetArray[i] = i; Quote: } If it is really important for you to return an array, you can do it. You use a Variant in VB and a VARIANT in C. It is fairly messy though and I don't have an example immediately to hand. Post back if you really want to see this and I'll try and dig up an example. HTH Peter Quote: > Hello- > I am having problems returing an array in a VB application when I a function > in a c++ DLL. I get a referenced memory error. I know the DLL is being > called correctly, but an error occurs at the point of returning the array. > Here is a snipit of code from the VB and VC++ applications. Thanks in > advance for any help! > '******************VB6.0 > Code************************************************************* > Dim RetArray() As Integer > ReDim RetArray(intNumBytes) 'redim the array that is expected > RetArray = ReturnArray(intNumBytes) 'call function in dll, return > type=array of integers '*********************************************************************** - Hide quoted text - - Show quoted text - Quote: > ********************* > file://*****************VC++6.0 > Code*********************************************************** > int * Add::ReturnArray(int numberbytes) > { > int Value[100]; > for(short int i=0;i<numberbytes;i++) > { > Value[i] = i; > } > return(Value); file://******************************************************************* * - Hide quoted text - - Show quoted text - Quote: > ************************ > Best Regards, > Matt Van Bergen
Tue, 22 Jan 2002 03:00:00 GMT

ami.. #4 / 4	VB calling C++ DLL returning an array?? Try this URL: http://support.microsoft.com/support/kb/articles/Q 177/2/18.ASP Quote: > Matt, > Try something like this: > Private Sub MyArrExample lib "MyDLL.dll" (byval NumItems as Integer, ByRef Quote: > RetArray As Integer) > and use something like: > Redim RetArr(14) as Integer > MyArrExample 15, RetArr(0) > The C++ end would be something like: > extern "C" void WINAPI MyArrExample(short iNumItems, short lpsRetArray) Quote: > { > short i; > for (i = 0; i < iNumItems; i++) > lpsRetArray[i] = i; > } > If it is really important for you to return an array, you can do it. You Quote: > use a Variant in VB and a VARIANT in C. It is fairly messy though and I Quote: > don't have an example immediately to hand. Post back if you really want to Quote: > see this and I'll try and dig up an example. > HTH > Peter > > Hello- > > I am having problems returing an array in a VB application when I a Quote: > function > > in a c++ DLL. I get a referenced memory error. I know the DLL is being Quote: > > called correctly, but an error occurs at the point of returning the array. Quote: > > Here is a snipit of code from the VB and VC++ applications. Thanks in Quote: > > advance for any help! > > '******************VB6.0 Code****************************************** *************** Quote: > > Dim RetArray() As Integer > > ReDim RetArray (intNumBytes) 'redim the array that is Quote: > expected > > RetArray = ReturnArray(intNumBytes) 'call function in dll, return Quote: > > type=array of integers > '******************************************* ************************ Quote: > > ********************* > > file://*****************VC++6.0 Code****************************************** ************* Quote: > > int * Add::ReturnArray(int numberbytes) > > { > > int Value[100]; > > for(short int i=0;i<numberbytes;i++) > > { > > Value[i] = i; > > } > > return(Value); file://***************************************** ********************** Quote: > * > > ************************ > > Best Regards, > > Matt Van Bergen Sent via Deja.com http://www.deja.com/ Share what you know. Learn what you don't.
Mon, 18 Feb 2002 03:00:00 GMT

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