lua的ipair与pair的区别

Lua nested table iteration:

lua: 

tbl1 = {  
       { a = "aa",b = "bb", c = "cc"},
       { d= "dd", e = "ee", f = "ff"},
      }
tbl2 = {  
       { aa = "aaa",bb = "bbb", cc = "ccc", gg = { g1 = "g1g1",g2 = "g2g2"},},
       { dd = "ddd", ee = "eee", ff = "fff"},   
      }

C: code snippet：　

lua_pushstring(L, "hello world1");
lua_pushstring(L, "hello world12"); 
lua_pushstring(L, "hello world123");
Lua_pushvalue(L, 1);


Lua_getglobal(L, "tbl1");
t1 = lua_gettop(L); 


lua_getglobal(L, "tbl2");
T2 = lua_gettop(L); 


table_dump(L, t1, 3)　　　　
table_dump(L, t2, 3);

-    int lua_next (lua_State *L, int index);     index， 表不需要在栈顶

-   多重表格的遍历： lua_next是 先弹出1个元素，压入2个元素key-value,  lua_pushnil仅仅是为了配合这- pop(1) push(2), pop(1) 操作而做的“无用操作”.

-   多重表格，碰到子表时，先是子表本身的key,值value是 table, 然后再说lua_next子表的内部元素。

-   循环时注意栈的平衡

/* Print a Lua table. depth_limit is the limit on recursive printing of
   subtables. */
static void table_dump (lua_State *L, int idx, int depth_limit)
{
  idx = lua_absindex(L, idx);
  assert(lua_type(L, idx) == LUA_TTABLE);
  printf("{");
  for (lua_pushnil(L);; /*lua_next(L, idx); lua_pop(L, 1)*/)    //分开为了调试，利用lua_gettop(L)查看栈长度，需要刷新
  {
    if ( lua_next(L, idx) <=0 ) break;

    value_dump(L, -2, depth_limit - 1);
    printf(" = ");
    value_dump(L, -1, depth_limit - 1);
    printf(", ");

    lua_pop(L, 1);
  }
  printf("}");
}

/* Print a Lua value. depth_limit controls the depth to which tables will be
   printed recursively (0 for no recursion). */
void value_dump (lua_State *L, int idx, int depth_limit)
{
  int t ;

  idx = lua_absindex(L, idx);  
  t = lua_type(L, idx);

  switch (t)
  {
    case LUA_TSTRING:  /* strings */
      printf("'%s'", lua_tostring(L, idx));
      break;
    case LUA_TBOOLEAN:  /* booleans */
      printf(lua_toboolean(L, idx) ? "true" : "false");
      break;
    case LUA_TNUMBER:  /* numbers */
      printf("%g", lua_tonumber(L, idx));
      break;
    case LUA_TTABLE:
      if (depth_limit > 0)
        table_dump(L, idx, depth_limit);
      else
        printf("table: %p", lua_topointer(L, idx));
      break;
    case LUA_TTHREAD:
    case LUA_TFUNCTION:
    case LUA_TUSERDATA:
    case LUA_TLIGHTUSERDATA:
      printf("%s: %p", lua_typename(L, t), lua_topointer(L, idx));
      break;
    default:  /* other values */
      printf("%s", lua_typename(L, t));
      break;
  }
}