I’m using Linux with GTK, writing an application in C, and need to retrieve data from a Libreoffice Calc file.
Save the file in CSV format, this will be much easier. You can automate the process in a small bash script, converting first the file to CSV, then launching your program on the converted file.
ODS is just a zip apchive with some xml files inside. Then you can unzip needed XML from ODS to memory and work with it