ngx_http_process_header_line function in source code (no replies)

Hi,
I'm browsing through the source code of the project, and looked at ngx_http_request.c where the function ngx_http_process_header_line() creates a pointer to a pointer to a large struct(ngx_http_request_t) containing a smaller one(ngx_http_headers_in_t), containing yet another one.

ngx_http_process_header_line(ngx_http_request_t *r, ngx_table_elt_t *h, ngx_uint_t offset) {
ph = (ngx_table_elt_t **) ((char *) &r->headers_in + offset);
// ... then check if ph is NULL, and if so point it to h
}


Why is it done in this way? It seems quite complex and error prone, doesen't it?
Is there any reason something like this wasn't done instead?

(where range are ONE of those structures in headers_in that are a ngx_table_elt_t)
if(r->headers_in->range == NULL) {
r->headers_in->range = h;
}