XLW is a C++ wrapper for the Excel C API described in the Microsoft Excel 97 Developer's Kit. It makes xll programming automatic. Its powerful interface will empower your C, C# or C++ numerics by embedding them in Excel just like the built-in functions.
Read data from Excel 97+ spread sheets without Microsoft! Provides an API to write applications that read Excel documents. The xlreader tool converts data to tab delimited, CSV or SQL inserts. Written in C. Based on the the Java version by Andrew Khan.