Lucene4c is a port of the Lucene search engine to C, built on top of the Apache Portable Runtime.
Unlike some other Lucene ports, Lucene4c does not stick to the API used in the original Java based Lucene when a more idiomatic APR and C API makes more sense. The goal is to remain compatible with the on-disk format used by Java Lucene (currently that of Lucene 1.4.x) but to provide an API that makes sense to programmers used to coding in C with APR.
Currently Lucene4c is read-only, and only the lowest level portions of the search engine has been implemented. The goal is to implement the remaining parts of the search side of Lucene4c first, and then to begin work on indexing support. In the meantime the Java Lucene must be used to create the index searched by Lucene4c.
In order to make effective use of Lucene4c you will need to understand how to use APR, which has its own API documentation at http://apr.apache.org/docs/apr/.