Excel12 vs Excel4

Excel12 and Excel12v ensure backwards compatibility with Excel 11 (2003) and earlier.

Excel12

This is a callback function that allows the DLL to call Excel.
Excel 2007 and later.
uese the XLOPER12 data structure
uese UNICODE based strings

int Excel12(int iFunction, 
            xloper12 *pxRes, 
            int iCount, 
            xloper12 *pxModuleText, 
            xloper12 *pxProcedure, 
            xloper12 *pxTypeText, 
            xloper12 *pxFunctionText, 
            xloper12 *pxArgumentText, 
            xloper12 *pxMacroType, 
            xloper12 *pxCategory, 
            xloper12 *pxShortcutText, 
            xloper12 *pxHelpTopic, 
            xloper12 *pxFunctionHelp, 
            xloper12 *pxArgumentHelp1, 
            ..) 

iFunction - xlfRegister
pxRes - A pointer that will hold the result
iCount - The number of arguments that are being passed in
pxModuleText -
pxProcedure -
pxTypeText -
pxFunctionText -
pxArgumentText - (Optional)
pxMacroType -
pxCategory -
pxShortcutText -
pxHelpTopic -
pxFunctionHelp -
pxArgumentHelp1 - Argument descriptions for each argument

All functions must be registered using the xlfRegister function from the C API

Excel12v

The Excel12 callback function provides arguments that are provided as a list of seperate arguments.
The Excel12v callback function provides arguments that are provided as an array.

int Excel12v(int iFunction, 
             xloper12 *pxRes, 
             int iCount, 
             xloper12 *pxArgs[]) 

iFunction - xlfRegister
pxRes - A pointer that will hold the result
iCount - The number of arguments that are being passed in
pxArgs - The array of arguments

LPXLOPER12

In most cases the prototype is written as:

int Excel12v(int iFunction, xloper12 *pRetVal, int count, xloper12 *args[]); 

but sometimes it is written as:

int Excel12v(int iFunction, LPXLOPER12 operRes, int count, xloper12 *args[]); 

This is just to represent that the argument is a pointer without having to include the asterisk (*)

XLOPER12 data type

This i s a multi-type data structure that can represent any type of worksheet data type.

FP12 data type

This is a two-dimensional floating point array structure that supports all the rows and columns

Excel4

Excel 2003 and earlier.
uese the XLOPER data structure
uses ASCII based strings