#include <mongoc/mongoc.h>
typedef struct _mongoc_gridfs_file_list_t mongoc_gridfs_file_list_t;

mongoc_gridfs_file_list_t *list;
mongoc_gridfs_file_t *file;
list = mongoc_gridfs_find (gridfs, query);
while ((file = mongoc_gridfs_file_list_next (list))) {
   do_something (file);
   mongoc_gridfs_file_destroy (file);
}
mongoc_gridfs_file_list_destroy (list);