RE: Simple Function Call From C language

[Thijs Schreijer <thijs@...>]

> -----Original Message-----
> From: lua-l-bounces@lists.lua.org [mailto:lua-l-bounces@lists.lua.org] On
> Behalf Of Austin Einter
> Sent: dinsdag 24 juni 2014 9:58
> To: Lua mailing list
> Subject: Re: Simple Function Call From C language
> 
> Hi Sean
> Your example worked pretty good.
> Thanks.
> I have some more doubt. If I want to avoid function stuff, just execute
> chunk, and get the result in C code, how best I can do it.
> Wrote below code, and working ok, please let me know if there is a better
> way to do it.
> And my MAJOR worry is this way am I bringing up any issue in stack (in C or
> in Lua) content, how do I make sure I am not messing up with stack content.

What are you exactly worried about? If you're writing code in C, then the stack is only one of your lesser concerns I would think.

> 
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <lua5.2/lua.h>
> #include <lua5.2/lualib.h>
> #include <lua5.2/lauxlib.h>
> 
> const char *c_function = "local a=5 local b=10 local c=a+b return c";
> 
> int main(void)
> {
>   lua_State *L;
>   int        r;
> 
>   L = (lua_State *) luaL_newstate();
>   luaL_openlibs(L); /* open all built-in Lua libraries */
>   luaL_dostring(L,c_function);
>   r = luaL_checkinteger(L, -1);
>   printf("\nResult = %d",r);
>   lua_close(L);
>   return EXIT_SUCCESS;
> }
> 
> 
> 
> 
> On Tue, Jun 24, 2014 at 9:12 AM, Sean Conner <sean@conman.org> wrote:
> It was thus said that the Great Austin Einter once stated:
> > Hi
> > Thanks a lot. Referring your links I could do a small test program.
> However
> > I am not able to get the output of lua function in C code. Here is my
> > example code. Please let me know, how to collect the lua function output
> in
> > C code.  After I call lua_loadstring, I want to print function output in
> > Code.., please let me know how to do it...
> #include <stdio.h>
> #include <stdlib.h>
> #include <lua.h>
> #include <lualib.h>
> #include <lualib.h>
> 
> const char *c_function = "function fact(n) if n == 0 then return 1 else
> return n * fact(n-1) end end"
> 
> int main(void)
> {
>   lua_State *L;
>   int        r;
> 
>   L = luaL_newstate();
>   luaL_openlibs(L); /* open all built-in Lua libraries */
> 
>   /*------------------------------------------------------------------------
>   ; the following two lines are basically luaL_dostring().  The first line
>   ; compiles the given Lua code into Lua bytecode and returns the result on
>   ; the Lua stack (not to be confused with the C stack---they are
>   ; different).  For the example above, the resulting code needs to be
>   ; executed to defien the fact() function.  Since luaL_loadstring() returns
>   ; the compiled code on the Lua stack, we can simply call lua_pcall() to
>   ; execute it.
>   ;
>   ; You might think that the function fact() will be defined at this point,
>   ; but no, all that's been done by luaL_loadstring() is to generate the
>   ; code that will define the fact() function.
>   ;------------------------------------------------------------------------
> */
> 
>   luaL_loadstring(L,c_function);
>   lua_pcall(L,0,0,0);
> 
>   /*-----------------------------------------------------------------------
>   ; now that we have fact() defined, we can now call it.  This just follows
>   ; the example given for the description of lua_call() in the manual.
>   ;----------------------------------------------------------------------*/
> 
>   lua_getglobal(L,"fact");      /* this is our function, defined globally */
>   lua_pushinteger(L,4);         /* this call fact(4)                    */
>   lua_call(L,1,1);              /* call fact, with one argument, and expect
> one result */
> 
>   r = luaL_checkinteger(L,-1);  /* the top of the Lua stack should contain
> our result */
>   printf("Factorial: %d",r);
> 
>   lua_close(L);
>   return EXIT_SUCCESS;
> }
> 
>   -spc
>