Data-access like Data[x]["Key"] = Value

Engines and Middleware Programming

Started by Dummie June 17, 2010 05:00 PM

3 comments, last by Matthew Shockley 13 years, 10 months ago

Dummie

100

Author

June 17, 2010 05:00 PM

Hey,

I like to make some data of my program accessible from Lua like that:

Data[x]["Key"] = Value;

I think this is the same:

Data[x].Key = Value;

I already tried it with the following code:

lua_newtable(l);        lua_pushinteger(l, 1);        lua_newtable(l);            lua_newtable(l);                lua_pushstring(l, "k1");                lua_pushstring(l, "v1");                lua_settable(l, -3);            lua_newtable(l);                lua_pushstring(l, "k2");                lua_pushstring(l, "v2");                lua_settable(l, -3);            lua_settable(l, -3);        lua_settable(l, -3);

Unfortunately nothing happens when I access the created table from Lua. It seems my Code is not right. What could be the problem? Where is the mistake?

Greetings

Matthew Shockley

100

June 17, 2010 09:03 PM

I may be wrong, but I believe you have to settable after every time you push a value.

If I asked you for a hundred dollars would the answer to that question be the same as the answer to this question?

m_switch

234

June 18, 2010 05:23 PM

Quote:Original post by Matthew Shockley
I may be wrong, but I believe you have to settable after every time you push a value.

You are wrong. settable consumes two values from the stack with each call. You should really test this or at least look at the documentation (which clearly suggests that this is not the case) before providing advice.

Quote:Original post by Dummie
Data[x]["Key"] = Value;
I think this is the same:
Data[x].Key = Value;

It is, the second way is just syntactic sugar for the first. You'll find that Lua is a very sugary language.

Quote:
Original post by Dummie
Unfortunately nothing happens when I access the created table from Lua.

Define "nothing".

Quote:
It seems my Code is not right. What could be the problem? Where is the mistake?

You're pushing strings onto the stack as values when you want to push a table. This is one way to do it, here I've commented what would be on the top of the stack at each point.

lua_newtable(L); //Datalua_newtable(L); //Data, subDatalua_pushinteger(L, 1); //Data, subData, 1lua_pushvalue(L, -2); //Duplicate subData - Data, subData, 1, subDatalua_settable(L, -4); //Data[1] = subData - (pops 2) Data, subData//setting a fieldlua_pushstring(L, "v1"); //Data, subData, "v1"lua_setfield(L, -2, "k1"); //subData["k1"] = "v1" - Data, subData//pop off the subtablelua_pop(L, 1); //Data