xls2xml is a free filter from Microsoft Excel to XML, and a free C library.
xls2xml is distributed under the terms of the GNU General Public License (GPL) to give an impulse to the Free Software. xls2xml distribution license is compatible with the Open Source definition.
Using the program xls2xml, you can extract the content of a file generated by Microsoft Excel and express its content using XML. A library written in C which is able to do the same is provided too.