container_of怖い

list.cpp

#include <iostream>
#include <vector>

using namespace std;

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

#define list_entry(ptr, type, member) container_of(ptr, type, member)

#define container_of(ptr, type, member) ({                  \
      const typeof(((type *)0)->member)* __mptr = (ptr);    \
      (type *)((char *)__mptr - offsetof(type, member)); })

struct List { List* next; };

struct V { int value;  List list; };
struct U { char value; List list; };
struct W { long long int value;  List list; };

void type_test_W()
{
  vector<W*> node_data;
  node_data.push_back(new W());
  node_data.back()->value = 'A';
  for (int size = 10; size--; )  {
    W* next = new W();
    next->value = node_data.size() + 'A';
    node_data.back()->list.next = &(next->list);
    node_data.push_back(next);
  }

  List* head = &(node_data.front()->list);

  for (int cnt = 10; cnt--; ) {
    W* t = list_entry((void*)head->next, W, list);
    cout << ">> " << t->value << endl;
    head = &(t->list);
  }
  return ;
}

void type_test_V()
{
  vector<V*> node_data;
  node_data.push_back(new V());
  node_data.back()->value = 'A';
  for (int size = 10; size--; )  {
    V* next = new V();
    next->value = node_data.size() + 'A';
    node_data.back()->list.next = &(next->list);
    node_data.push_back(next);
  }

  List* head = &(node_data.front()->list);

  for (int cnt = 10; cnt--; ) {
    V* t = list_entry((void*)head->next, V, list);
    cout << ">> " << t->value << endl;
    head = &(t->list);
  }
  return ;
}

void type_test_U()
{
  vector<U*> node_data;
  node_data.push_back(new U());
  node_data.back()->value = 'A';
  for (int size = 10; size--; )  {
    U* next = new U();
    next->value = node_data.size() + 'A';
    node_data.back()->list.next = &(next->list);
    node_data.push_back(next);
  }

  List* head = &(node_data.front()->list);

  for (int cnt = 10; cnt--; ) {
    U* t = list_entry((void*)head->next, U, list);
    cout << ">> " << t->value << endl;
    head = &(t->list);
  }
  return ;
}

int main(int argc, char *argv[])
{
  cout << offsetof(U, value) << endl; // 0
  cout << offsetof(U, list) << endl;  // 4
  cout << endl;

  type_test_U();
  cout << endl;
  type_test_V();
  cout << endl;
  type_test_W();
  cout << endl;

  return 0;
}