how do you access the nonzero elements in SeqAIJ matrices

I am working on a project where I would like to copy a sparse matrix in CSR format. I have tried MatGetRow() which works OK but I would really like to get pointers to the 3 arrays directly. I also tried MatGetRowIJ() which allows me to get the i and j arrays but I can't see how to access the nonzero elements. and finally I attempted to access the arrays directly like this: Mat_SeqAIJ *a = (Mat_SeqAIJ*)A->data; MatScalar *val = a->a; PetscInt *ptr = a->i; PetscInt *ind = a->j; However when accessing directly I get different values for ptr and SIGSEGV when accessing val or ind. also I get a bogus number for a->nz (134630032 instead of 21) Can someone please explain when I am doing wrong? Ahmed