Re: Pass pointer into LUA

["Nguyen Dang Quang" <quangnd412@...>]

Hi Pavel Antokolsky,
Thanks for your advice, it helps me very much.
----- Original Message ----- 
From: "Pavel Antokolsky aka Zigmar" <zigmar@gmail.com>
To: "Lua list" <lua@bazar2.conectiva.com.br>
Sent: Sunday, April 03, 2005 11:59 PM
Subject: Re: Pass pointer into LUA


> Here is simple example from my app. Note that this is not copy/paste
> (my companie's policy forbids it) so in may contain typos. This code
> is addition to my last message, which contained function exported to
> Lua that returned userdata to Lua script.
>
> This function receives userdata from Lua script, casts it back to C++
> object and performs some operation on it:
>
> int LuaCanvas::line_set(lua_State *lua)
> {
>     luaL_checktype(lua,1,LUA_TLIGHTUSERDATA);
>     QCanvasLine *line = static_cast<QCanvasLine*>(lua_touserdata(lua,1));
>     double x1 = luaL_checknumber(lua,2);
>     double y1 = luaL_checknumber(lua,3);
>     double x2 = luaL_checknumber(lua,4);
>     double y2 = luaL_checknumber(lua,5);
>
>     line->setPoints(x1,y1,x2,y2);
>     return 0;
> }
>
> and this is how is looks like from Lua script's point of view:
>
> --creating new line and assigning it to "myLine" variable (will
> contain "userdata" type)
> myLine = line_new()
> --passing it to other api func listed above
> line_set(myLine,100,100,200,200)
>
> Very simple :)
>
> Hope it helps you.
>
> On Apr 1, 2005 3:26 AM, Nguyen Dang Quang <quangnd412@yahoo.ca> wrote:
> > Hi Pavel Antokolsky,
> >
> >     Thank for replying me. Could you send me a sample code in with you
pass
> > an pointer to LUA and LUA store it in a variable and then LUA pass back
this
> > pointer to other C pointer. Thank you very much.
> >
> > ----- Original Message -----
> > From: "Pavel Antokolsky aka Zigmar" <zigmar@gmail.com>
> > To: "Lua list" <lua@bazar2.conectiva.com.br>
> > Sent: Thursday, March 31, 2005 7:00 PM
> > Subject: Re: Pass pointer into LUA
> >
> > > There is no need to use numerical type to store pointer, and sure it
> > > unsafe. There is a special datatype for passing pointers into lua:
> > > "light userdata".
> > > For more documentation see "lua_pushlightuserdata" and  #28.5 in
> > > "Programming in  Lua book".
> > >
> > > Here is a small code snipplet:
> > > The function exported to Lua that creates C++ object and returns
> > > userdata with pointer to it:
> > >
> > > int LuaCanvas::line_new (lua_state *lua)
> > > {
> > > QCanvasLine *line = new QCanvasLine(getCanvas(lua));
> > > lua_pushlightuserdata(lua,line)
> > > return 1;
> > > }
> > >
> > > "getCanvas()" function retrivies the pointer to LuaCanvas object (the
> > > exported method is static) stored in lua registry. If you are
> > > interested, I can also send you a snippled how this pointer is stored
> > > and retrivied.
> > >
> > >
> > >
> > > On Thu, 31 Mar 2005 16:35:15 +0700, Nguyen Dang Quang
> > > <quangnd412@yahoo.ca> wrote:
> > > > Hi,
> > > > I have a big problem with passing pinter to LUA. In LUA documents,
they
> > say
> > > > that programers can use LUA number (in fact a double type!) but it
> > sounds
> > > > not safe at all when storing pointer in a double number form! How
can I
> > > > solve this problem?
> > > >
> > > >
> > >
> > >
> > > --
> > > Best regards,
> > > Zigmar
> >
> >
>
>
> -- 
> Best regards,
> Zigmar