Method NLastChildren

cpp/src/arrow/c/bridge_test.cc:2630–2644

Create a stable C pointer to the N last structs in nested_structs_

  // Create a stable C pointer to the N last structs in nested_structs_
  struct ArrowArray** NLastChildren(int64_t n_children, struct ArrowArray* parent) {
    children_arrays_.emplace_back(n_children);
    struct ArrowArray** children = children_arrays_.back().data();
    int64_t nested_offset;
    // If parent is itself at the end of nested_structs_, skip it
    if (parent != nullptr && &nested_structs_.back() == parent) {
      nested_offset = static_cast<int64_t>(nested_structs_.size()) - n_children - 1;
    } else {
      nested_offset = static_cast<int64_t>(nested_structs_.size()) - n_children;
    }
    for (int64_t i = 0; i < n_children; ++i) {
      children[i] = &nested_structs_[nested_offset + i];
    }
    return children;
  }

  struct ArrowArray* LastChild(struct ArrowArray* parent = nullptr) {
    return *NLastChildren(1, parent);