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Thanks for this. Methinks that it it will be a commonly written piece of code for me and others, hence I think it (or something like it) should be Lua distro. 
DB

On 15/1/2010 10:32 AM, Peter Cawley wrote:

One way of implementing it, which is used to get the C equivalent of
"for k, v in pairs(t) do ... end": (MIT license, if anyone cares)
int luaL_pairs(lua_State *L, int index) {
   /* Start of iteration? */
   if (lua_isnil(L, -1)) {
     lua_checkstack(L, 2);
     if (luaL_getmetafield(L, index, "__pairs")) {
       lua_pushvalue(L, index);
       lua_replace(L, -4);
       lua_replace(L, -4);
       lua_pop(L, 1);
       lua_call(L, 1, 3);
       if(lua_isnil(L, -3)) {
         lua_pop(L, 2);
         lua_call(L, 0, 0);
       }
     }
   }
   /* Continuation of iteration */
   if(lua_isnil(L, -3)) {
     if (lua_next(L, index))
       return 1;
     lua_pop(L, 2);
     return 0;
   }
   else {
     lua_pushvalue(L, -3);
     lua_pushvalue(L, -3);
     lua_pushvalue(L, -3);
     lua_remove(L, -4);
     lua_call(L, 2, 2);
     if (lua_isnil(L, -2)) {
       lua_pop(L, 4);
       return 0;
     }
     return 1;
   }
}

Usage is then similar to, but not quite the same as, lua_next:
/* table is in the stack at index 't' */
lua_settop(L, lua_gettop(L) + 3); /* state variables and first key */
while (luaL_pairs(L, t) != 0) {
   /* uses 'key' (at index -2) and 'value' (at index -1) */
   printf("%s - %s\n",
          lua_typename(L, lua_type(L, -2)),
          lua_typename(L, lua_type(L, -1)));
   /* removes 'value'; keeps 'key' for next iteration */
   lua_pop(L, 1);
}

On Thu, Jan 14, 2010 at 11:20 PM, David Burgess<dabsoft@gmail.com>  wrote:

OK then. How about luaL_pairs()?

On 15/1/2010 9:50 AM, Luiz Henrique de Figueiredo wrote:


I think we should have lua_pairs() to match lua_next()


__pairs is not a core metamethod, just like __tostring: it is provided
by the base library. So, it cannot influence the C API.