The way DoString works in WoW

[tanis2000]

I'm trying to get my mind set on how DoString actually works in WoW and understand if I can use that to do what I want

I suppose that Lua_DoString is actually the same lua_dostring() that exists in LUA (and that appears to have been deprecated in 5.1+).

As far as I can tell from the manual Lua: 4.0 reference manual you pass a string with a chunk of LUA code and the interpreter executes it.

Lua_DoString pushes onto the stack any values eventually returned by the chunk and then it's up to me/us to retrieve them from the stack or just discard them.

Now, what I didn't understand is if this chunk of code once executed becomes part of the global code that has been loaded into the LUA interpreter and thus it's like if I loaded one more addon, so to speak or if it just gets discarded.

What I would like to use it for is to do things like this:

local function test()
	SetMapToCurrentZone()
	local continent = "test"..GetCurrentMapContinent()
	return continent
end

res = test()

Define a function that does something and returns something, execute it and then pop off the stack the return values. And of course I don't want to taint the global space.

Is that something viable or am I going in a completely wrong direction?

[Cypher]

It's different.

What everyone calls "DoString" is actually called FrameScript__Execute, which is a wrapper around the Lua funcs for executing code. FrameScript__Execute actually discards the return values on the stack afaik so you can't retrieve them. That's why people register a callback to be used as a 'wrapper'.

I'm no expert though, if you want more info then find someone who has reversed it to the point that they've reimplemented it (e.g. Greyman if he sees this thread, or maybe Amadmonk, I think he may have done it too).

[tanis2000]

Thanks Cypher!

I've been toying around with this stuff and I noticed that FrameScript__Execute is actually acting differently than I first thought (reason n.1 being that as you say, it's not just the standard lua_dostring)

As an example, I would expect that if I call

FrameScript__Execute("MyInputHandler(return 1,'a')")

I'd get as a result in the stack those two values.
Instead I find nothing.

But if I just do

FrameScript__Execute("MyInputHandler(1,'a')")

then I get the two values in the stack (although in reverse order compared to the original LUA DoString function).

I wonder if there's a way to actually access the original lua_dostring instead of having to call FrameScript__Execute passing your own wrapper as it seems that FrameScript__Execute is actually doing something with the code you pass, and if it likes it then it returns the values in reverse order. Now this is opening yet another hole in my mumblings.. are the other lua_gettop, lua_tostring functions actually those of the LUA interpreter or are they some other custom functions from Blizzard?

[MaiN]

FrameScript__Execute("MyInputHandler(return 1,'a')")

Eh, that's a LUA error. If you want to do it like that you need to define a dynamic function.

FrameScript__Execute("MyInputHandler((function() return 1, 'a' end)()")

[berserk85]

From my exp i can say that lua_gettop and lua_tostring act like original lua function.
If you are trying to execute a lua function without DoString() you can try with lua_pcall or lua_call ...

void Lua_CallVarg(const char *func, const char *sig, ...)
{    //http://www.lua.org/pil/25.3.html

			void *L;
			L = GetLuaState();
			//DBGLOG( (PDWORD)L );
			char* str;
			 va_list vl;
			  int narg, nres;  /* number of arguments and results */
			  va_start(vl, sig);
			  Lua_Getglobal(L, func);  /* get function */
		    
			  /* push arguments */
			  narg = 0;
			  while (*sig) {  /* push arguments */
				switch (*sig++) {
		    
				  case 'd':  /* double argument */
					Lua_pushnumber(L, va_arg(vl, double));
					break;
		    
				  case 'i':  /* int argument */
					Lua_pushnumber(L, va_arg(vl, int));
					break;
		    
				  case 's':  /* string argument */
					str = va_arg(vl, char *);
					Lua_pushstring(L, str,strlen(str));
					break;
		    
				  case '>':
					goto endwhile; // ugly conditional branch
		    
				  default:
					  DBGLOG( "Lua_CallVarg : Invalid option " << *(sig - 1) );
				}
				narg++;
				//luaL_checkstack(L, 1, "too many arguments");
			  } endwhile:
		    
			  /* do the call */
			  nres = strlen(sig);  /* number of expected results */
			  unsigned int size;
			  if (Lua_pcall(L, narg, nres, 0) != 0)  /* do the call */
				DBGLOG("error running function " << func << " " << Lua_tostring(L, -1,&size) );
		    
			  /* retrieve results */
			  nres = -nres;  /* stack index of first result */
			  while (*sig) {  /* get results */
				switch (*sig++) {
		    
				  case 'd':  /* double result */
					if (!Lua_isnumber(L, nres))
					  DBGLOG ( "wrong result type");
					*va_arg(vl, double *) = Lua_tonumber(L, nres);
					break;
		    
				  case 'i':  /* int result */
					if (!Lua_isnumber(L, nres))
					  DBGLOG ( "wrong result type");
					*va_arg(vl, int *) = (int)Lua_tonumber(L, nres);
					break;
		    
				  case 's':  /* string result */
					if (!Lua_isstring(L, nres))
					  DBGLOG ( "wrong result type");
					unsigned int size;
					*va_arg(vl, const char **) = Lua_tostring(L, nres, &size);
					break;
		    
				  default:
					DBGLOG ( "invalid option " << *(sig - 1));
				}
				nres++;
			  }
			  va_end(vl);
}

and call the GetCurrentMapContinent() with

int *i;
Lua_CallVarg("GetCurrentMapContinent",">i",i);

[tanis2000]

Eh, that's a LUA error. If you want to do it like that you need to define a dynamic function.

Shame on me for taking for granted the sample code from the lua-users wiki :-P
lua-users wiki: Getting Values From Lua

With your code it actually works of course.

So I guess I could actually wrap any piece of code into a dynamic function and use that with FrameScript_Execute. I'll give it a go with something a bit more complex to see what happens.

As a side note, do you have any reference to how tables returned by dostring are stored in the stack?


@berserk85: if there's a way to get what I need by using FrameScript_Execute, I'll stick to that.. otherwise I guess I'll switch to lua_pcall. Thanks for the code sample though!

[MaiN]

Shame on me for taking for granted the sample code from the lua-users wiki :-P
lua-users wiki: Getting Values From Lua

Eh, FrameScript__Execute != lua_dostring (as Cypher already told you) - IIRC lua_dostring defines a dynamic function internally, and calls that.

As a side note, do you have any reference to how tables returned by dostring are stored in the stack?

I really don't know. When I need to return a table I use unpack. Eg.:

Lua.ReturnValues("local testTable = {\"test\", \"test2\"} return testTable")

That returns an empty array.

However, using

Lua.ReturnValues("local testTable = {\"test\", \"test2\"} return unpack(testTable)")

will return an array of 2 items (test and test2 obviously).

[Nesox]

Take à look at lua_load and lua_pcall