C API Callback Functions Excel4, Excel12
The Excel4 and Excel12 functions are provided to enable DLLs to call an internal Microsoft Excel worksheet function, macro sheet function or command, or XLL-only special function or command. All recent versions of Excel support the Excel4 function. Starting in Excel 2007 the Excel12 function is supported. Both functions are provided in two forms:
A variable-length argument list form (Excel4/Excel12)
An array-of-arguments form (Excel4v/Excel12v)
Except for the way in which arguments are passed to these callbacks, the two forms are functionally equivalent. The basic concepts for both forms are fully described in Excel4/Excel12. Excel4v/Excel12v covers other issues about this form.