C++ 存储和访问指向 struct 的指针数组

我正在处理一个用例，其中我希望有dynamic array个指针，这些指针指向某种类型的 struct .

我注意到一些奇怪的行为，我希望有人能帮忙澄清.

首先，我将使用static array个指针来分享passing test.

TEST test_f_chunk_array(void) {
  f_chunk* first;
  f_chunk* second;

  test_f_chunk_array_setup(&first, &second);

  // just validating that the setup is working as expected.
  ASSERT_EQ_FMT(1ul, (*first->first)->bytes->offset, "%zu");
  ASSERT_EQ_FMT(5ul, (*second->first)->next->bytes->offset, "%zu");
  ASSERT_EQ_FMT(6ul, (*second->first)->bytes->offset, "%zu");

  f_chunk* arr[2] = {NULL};
  arr[0] = first;
  arr[1] = second;

  // original pointers were not mutated, not surprising.
  ASSERT_EQ_FMT(1ul, (*first->first)->bytes->offset, "%zu");
  ASSERT_EQ_FMT(5ul, (*second->first)->next->bytes->offset, "%zu");
  ASSERT_EQ_FMT(6ul, (*second->first)->bytes->offset, "%zu");

  f_chunk* first_chunk = arr[0];
  f_chunk* second_chunk = arr[1];

  // awesome, retrieval works as expected.
  ASSERT_EQ_FMT(1ul, (*first_chunk->first)->bytes->offset, "%zu");
  ASSERT_EQ_FMT(5ul, (*second_chunk->first)->next->bytes->offset, "%zu");
  ASSERT_EQ_FMT(6ul, (*second_chunk->first)->bytes->offset, "%zu");

  PASS();
}

现在，对于使用dynamic array的failing test人，我注意到了一些我不太理解的行为.

TEST test_f_chunk_dynamic_array(void) {
  f_chunk* first;
  f_chunk* second;

  test_f_chunk_array_setup(&first, &second);

  // just validating that the setup is working as expected.
  ASSERT_EQ_FMT(1ul, (*first->first)->bytes->offset, "%zu");
  ASSERT_EQ_FMT(5ul, (*second->first)->next->bytes->offset, "%zu");
  ASSERT_EQ_FMT(6ul, (*second->first)->bytes->offset, "%zu");

  // using dynamic array.
  size_t size = 2;
  f_chunk** arr = malloc(size * sizeof(f_chunk*));

  arr[0] = first;
  arr[1] = second;

  /*
    sanity check, I wouldn't expect for the underlying struct to be mutated
    as the array would only assign a copy of the pointer value?  
  */
  ASSERT_EQ_FMT(1ul, (*first->first)->bytes->offset, "%zu");
  // ^^^^ segfaults.

  ASSERT_EQ_FMT(5ul, (*second->first)->next->bytes->offset, "%zu");
  ASSERT_EQ_FMT(6ul, (*second->first)->bytes->offset, "%zu");

  f_chunk* first_chunk = arr[0];
  f_chunk* second_chunk = arr[1];

  // this doesn't work either.
  ASSERT_EQ_FMT(1ul, (*first_chunk->first)->bytes->offset, "%zu");
  ASSERT_EQ_FMT(5ul, (*second_chunk->first)->next->bytes->offset, "%zu");
  ASSERT_EQ_FMT(6ul, (*second_chunk->first)->bytes->offset, "%zu");

  PASS();
}

很明显，我错过了什么，但我不确定是什么.我认为分配空间并在其上存储指针地址不会改变指针所指向的 struct .

Edit个

分享设置，如果它有助于澄清.

void test_f_chunk_array_setup(f_chunk** first, f_chunk** second) {
  f_bytes* first_bytes;
  f_bytes* second_bytes;
  f_bytes* third_bytes;
  f_bytes_new(&first_bytes, true, 1ul);
  f_bytes_new(&second_bytes, true, 5ul);
  f_bytes_new(&third_bytes, false, 6ul);


  f_bytes_node* first_node;
  f_bytes_node* second_node;
  f_bytes_node* third_node;
  f_bytes_node_new(&first_node, first_bytes);
  f_bytes_node_new(&second_node, second_bytes);
  f_bytes_node_new(&third_node, third_bytes);

  first_node->next = NULL;
  second_node->next = NULL;
  third_node->next = second_node;

  f_chunk* first_chunk;
  f_chunk* second_chunk;

  f_chunk_new(&first_chunk, 1, &first_node, &first_node);
  f_chunk_new(&second_chunk, 2, &third_node, &second_node);

  *first = first_chunk;
  *second = second_chunk;
}

Second Edit个

最小可重复示例:https://godbolt.org/z/6c8z7coYq