TOMS515 is a MATLAB library which lists the subsets of size K selected from a set of size N, by Bill Buckles, Matthew Lybanon.
TOMS515 is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version and a Python version.
SUBSET, a MATLAB library which enumerates combinations, partitions, subsets, index sets, and other combinatorial objects.
Original FORTRAN77 version by Bill Buckles, Matthew Lybanon. MATLAB version by John Burkardt.
You can go up one level to the MATLAB source codes.