LibSBML is an open-source programming library to help you read, write,
manipulate, translate, and validate SBML files and data streams. It is
not an application itself (though it does come with example programs),
but rather a library you can embed in your own applications.

LibSBML understands all Levels and Versions of SBML, as well as the
SBML Layout proposal by Gauges, Rost, Sahle and Wegner. It's written in
ISO C and C++ but can be used from all the languages listed in the
right-hand box.