Although the main branch of SWIG cannot generate C wrappers for C++ API (the SWIG documentation quoted in the question is a bit misleading), there is a SWIG branch created during Google Summer of Code 2008 and available at https://swig.svn.sourceforge.net/svnroot/swig/branches/gsoc2008-maciekd/ which does just that. I have found the answer here: C++ to C Wrapper using SWIG (for FLTK)
