If you are interested in learning about Microsoft Office Excel 2007 features that affect XLL add-ins and enable new XLL functionality, as well as changes to the XLL C API itself, we just published a great article by Steve Dalton that will help you get started.
The intended audience for this article consists of Microsoft Visual C and Microsoft Visual C++ developers who already have experience developing Microsoft Office Excel add-ins, or XLLs. This article is not an introduction to XLL development although a brief overview is included. To make the most of this article, readers should be familiar with:
- C and C++ language concepts and constructs. Code examples are written in C++.
- Building DLLs that export functions.
- The XLOPER data structure and other Excel data types, such as the floating point matrix structure (FP).
- The add-in manager interface functions, such as xlAutoOpen and xlAutoClose.
- XLOPER memory management (xlAutoFree, xlFree, and the use of xlbitDLLFree and xlbitXLFree).
Read the article here: http://msdn2.microsoft.com/en-us/library/aa730920.aspx