It is not Singulars main goal to create a C++ library,
but, yes, it is possible, and some programs use Singular as a C++ library.
Once you have build a stand alone Singular, the Makefile in ./Singular
provides the targets libsingular.a and libsingular.so
which contain all Singular functions. (The problems with coexisting
memory managers have been solved).
Rudimentary documentation of the internals can be found at
http://www.mathematik.uni-kl.de/ftp/pub ... natomy.tgz