[petsc-users] Correct use of VecGetArray with std::vector

[Zane Charles Jakobs]

Hi PETSc devs,

I'm writing some C++ code that calls PETSc, and I'd like to be able to
place the result of VecGetArray into an std::vector and then later call
VecRestoreArray on that data, or get the same effects. It seems like the
correct way to do this would be something like:

Vec x;
std::vector<PetscScalar> vals, idx;
int   num_vals, global_offset;
PetscErrorCode ierr;
...
/* do some stuff to x and compute num_vals  and global_offset*/
...
vals.resize(num_vals);
idx.resize(num_vals);
std::iota(idx.begin(), idx.end(), global_offset);
ierr = VecGetValues(x, num_vals, idx.data(), vals.data());CHKERRQ(ierr);
/* do stuff to vals */
...
ierr = VecSetValues(x, num_vals, idx.data(), vals.data(), [whatever insert
mode]);CHKERRQ(ierr);
idx.clear();
vals.clear();

Is that correct (in the sense that it does what you'd expect if you
replaced the vectors with pointers to indices/data and used
VecGet/RestoreArray() instead of VecGet/SetValues, and it doesn't violate
any of std::vector's invariants, e.g. by reallocating its memory)? If not,
is there a "normal" way to do this?

Thanks!

-Zane Jakobs
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