How to replicate vector in c?

Question

In the days before c++ and vector/lists, how did they expand the size of arrays when they needed to store more data?

Answer 1

You can see implementation vc_vector:

struct vc_vector {
  size_t count;
  size_t element_size;
  size_t reserved_size;
  char* data;
  vc_vector_deleter* deleter;
};

...

vc_vector* vc_vector_create_copy(const vc_vector* vector) {
  vc_vector* new_vector = vc_vector_create(vector->reserved_size / vector->count,
                                           vector->element_size,
                                           vector->deleter);
  if (unlikely(!new_vector)) {
    return new_vector;
  }

  if (memcpy(vector->data,
             new_vector->data,
             new_vector->element_size * vector->count) == NULL) {
    vc_vector_release(new_vector);
    new_vector = NULL;
    return new_vector;
  }

  new_vector->count = vector->count;
  return new_vector;
}

To use it:

vc_vector* v1 = vc_vector_create(0, sizeof(int), NULL);
for (int i = 0; i < 10; ++i) {
  vc_vector_push_back(v1, &i);
}

// v1 = 0 1 2 3 4 5 6 7 8 9

vc_vector* v2 = vc_vector_create_copy(v1);

// v2 = 0 1 2 3 4 5 6 7 8 9 (copy of v1)

// to get pointer to int:

const int* v2_data = vc_vector_data(v1);