1. VBA to C: Pratfalls and Perils XLDevC London 2012
Charles Williams
Decision Models 1996
Author of FastExcel
Co-author of Name Manager
VBA to C - Pratfalls and Perils
20/09/2018

2. VBA to C: Pratfalls & Perils
FastExcel functions
8000 lines of VBA/VB6 Automation UDFs
Excel 2010
64-bit
Multi-threading/ multiple cores
VB6 is dead-end
My journey from VBA to C
VBA to C - Pratfalls and Perils
20/09/2018

3. Expectation Steep Learning Curve Memory Management Pointers
Low level Language
Excel SDK
Buggy
Poorly documented
Uses complex Oper data structure
VBA to C - Pratfalls and Perils
20/09/2018

4. So minimise learning curve using
Planatech XLL+
Visual Studio 2010
C++ Primer Plus
Stephen Prata
XL Add-in Development in C++
Steve Dalton
VBA to C - Pratfalls and Perils
20/09/2018

5. XLL+ Function Wizard
VBA to C - Pratfalls and Perils
20/09/2018

6. XLL+ Function Wizard
VBA to C - Pratfalls and Perils
20/09/2018

7. C Code with Equivalent VBA
double AvTolXLL2_Impl(const CXlOper* theNumbers, double theTolerance) {
// End of generated code
//}}XLP_SRC
// TODO - set the value of xloResult, or return another value
// using CXlOper::RetXXX() or throw a CXlRuntimeException.
RW12 nRows=0; // Dim nRows as long
COL12 nCols=0; // Dim nCols as long
double dTemp=0.0,dAvTol=0.0; // Dim dTemp as double, dAvTol as double
RW12 Counter=0; // Dim Counter as long
// theNumbers is pointer to oper value array (P)// vArr=theNumbers.Value2
// get num of rows cols in input data
theNumbers->GetDims(nRows,nCols); //nRows=Ubound(vArr)nCols=Ubound(vArr,2)
// loop thru the input data
for (RW12 i=0; i<=nRows-1; i++) // For i=0 To nRows-1 Step 1
// curly brackets for a block of statements
// get value, (zero if not converted to double)
dTemp=theNumbers->Cell(i,0).ToDouble(); // dTemp=cdbl(vArr(i+1,1)
//compare to the tolerance
if (fabs(dTemp)>theTolerance) // If Abs(dTemp)>theTolerance Then
dAvTol += dTemp; // dAvTol=dAvTol+dTemp
Counter++; // Counter=Counter+1
}; // End If
}; // Next i
// return value if neither are zero:
// ! means NOT && means AND || means OR
if (dAvTol != 0.0 && Counter != 0) // If dAvtol<>0.0 and Counter<>0 then
return dAvTol/Counter; // AvTolXLL2=dAvtol/Counter
Else // else
return 0.0; // AvTolXLL2=0.0 ‘Note the ; ends the IF
} // End Function
VBA to C - Pratfalls and Perils
20/09/2018

8. The Journey so far … STL/BOOST/XLL+/VS2010
High-level language, rich framework
But lot to learn
Memory management not yet needed
Performance is good
Creating simple UDFs is easy …
VBA to C - Pratfalls and Perils
20/09/2018

9. Things I don’t (yet) understand
Strings
XLL & Excel Locales
Passing data between VBA & C
Oper data structure
Binary Names
Asynchronous functions …
VBA to C - Pratfalls and Perils
20/09/2018