Problems with callback from DLL invoked from VBA
I have to invoke a C++ function from VBA/Excel that does a callback. I've
isolated the problem I'm having in the code below. In the C++ (complied & linked to a DLL) I have: long __stdcall tryCB3(long n, long (*cbFunc)(long m)) { long r; r = cbFunc(n); // call back return r; } In the VBA I have: Private Declare Function tryCB3 Lib "SparkExUtilsDll.dll" _ (ByVal n As Long, ByVal theFunct As Any) As Long Public Function theCBFunc3(ByVal m As Long) As Long Debug.Print "In theCBFunc3" theCBFunc3 = m * m End Function Public Function tryCBDrv3() Dim n As Long Dim q As Long n = 2 q = tryCB3(2, AddressOf theCBFunc3) Debug.Print "n= " & CStr(n) Debug.Print "q= " & CStr(q) End Function When I step through tryCB3Drv it calls tryCB3, and then steps through theCBFunc3, all working as expected, but then crashes with a C++ error dialog saying the ESP was not preserved through a function call etc. Note that the it works without crashing if the callback function has no arguments, so it must be some problem with the way VBA is setting up the argument to theCBFunc3, vs. the way it's declared in C++. Any ideas? TIA Ed |
Problems with callback from DLL invoked from VBA
Change your C++ function to
long __stdcall tryCB3(long n,long(__stdcall *cbFunc)(long m)) -- Cordially, Chip Pearson Microsoft MVP - Excel Pearson Software Consulting, LLC www.cpearson.com "Jag Man" wrote in message ... I have to invoke a C++ function from VBA/Excel that does a callback. I've isolated the problem I'm having in the code below. In the C++ (complied & linked to a DLL) I have: long __stdcall tryCB3(long n, long (*cbFunc)(long m)) { long r; r = cbFunc(n); // call back return r; } In the VBA I have: Private Declare Function tryCB3 Lib "SparkExUtilsDll.dll" _ (ByVal n As Long, ByVal theFunct As Any) As Long Public Function theCBFunc3(ByVal m As Long) As Long Debug.Print "In theCBFunc3" theCBFunc3 = m * m End Function Public Function tryCBDrv3() Dim n As Long Dim q As Long n = 2 q = tryCB3(2, AddressOf theCBFunc3) Debug.Print "n= " & CStr(n) Debug.Print "q= " & CStr(q) End Function When I step through tryCB3Drv it calls tryCB3, and then steps through theCBFunc3, all working as expected, but then crashes with a C++ error dialog saying the ESP was not preserved through a function call etc. Note that the it works without crashing if the callback function has no arguments, so it must be some problem with the way VBA is setting up the argument to theCBFunc3, vs. the way it's declared in C++. Any ideas? TIA Ed |
Problems with callback from DLL invoked from VBA
Yes, that works. Thanks, Chip.
Now, moving closer to what I really need to do, I need to add an array argument to the callback function: long __stdcall tryCB3(long n,long(__stdcall *cbFunc)(long m, long *)) { .... long* x= new long[n]; .... r = cbFunc(n, x); ... delete [] x; return r; } And in the VB: Public Function theCBFunc4(ByVal m As Long, ByRef x() As Long) As Long Dim i As Integer Dim s As Long s = 0 For i = 0 To m - 1 s = s + x(i) Next i theCBFunc4 = s End Function But, it doesn't work. It crashes Excel when I call the tryCB3 function from VB. Any ideas? TIA Ed |
Problems with callback from DLL invoked from VBA
I'm not sure what the problem is. I suspect that it is because
VB/VBA uses SAFEARRAY structures rather than C-type arrays. You might have more luck posting this in one of the Visual C newsgroups. -- Cordially, Chip Pearson Microsoft MVP - Excel Pearson Software Consulting, LLC www.cpearson.com "Jag Man" wrote in message ... Yes, that works. Thanks, Chip. Now, moving closer to what I really need to do, I need to add an array argument to the callback function: long __stdcall tryCB3(long n,long(__stdcall *cbFunc)(long m, long *)) { ... long* x= new long[n]; ... r = cbFunc(n, x); .. delete [] x; return r; } And in the VB: Public Function theCBFunc4(ByVal m As Long, ByRef x() As Long) As Long Dim i As Integer Dim s As Long s = 0 For i = 0 To m - 1 s = s + x(i) Next i theCBFunc4 = s End Function But, it doesn't work. It crashes Excel when I call the tryCB3 function from VB. Any ideas? TIA Ed |
Problems with callback from DLL invoked from VBA
Thanks, Chip. When I get to the bottom of it I'll post the solution.
Ed "Chip Pearson" wrote in message ... I'm not sure what the problem is. I suspect that it is because VB/VBA uses SAFEARRAY structures rather than C-type arrays. You might have more luck posting this in one of the Visual C newsgroups. -- Cordially, Chip Pearson Microsoft MVP - Excel Pearson Software Consulting, LLC |
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