Re: Rerun of the same chunk via lua_pcall

[Jonathan Castello <twisolar@...>]

The call to lua_getglobal pushes the global you wanted onto the stack,
so the stack index -1 refers to the result, not the chunk (which would
now probably be -2).

It helps to add comments next to each lua_* line showing what the
current status of the stack is, so you can always tell what you need
to do. For example:

----
/* L: chunk */
lua_pushvalue(L, -1); /* L: chunk, chunk */
lua_pcall( L, 0, 0, 0 ); /* L: chunk */
lua_getglobal( L, "result" ); /* L: chunk, result */
---

Simplest thing to do would be to add a lua_pop(L, 1) after you're done
with each result, to remove it from the stack..

~Jonathan

On Sat, Aug 21, 2010 at 1:44 PM, Joachim Buermann <jbuermann@iftools.com> wrote:
> Hello Duncan,
>
> WOW!!! Thank you very much for your fast response. Unfortunatelly I did forget
> some detail in my example. For it your hint works great, but the little
> detail is:
>
> I need something like this in a loop or triggered by some user action:
>
> while(...) {
>
>        lua_pushvalue(L, -1);
>
>        lua_pcall( L, 0, 0, 0 );
>
>        lua_getglobal( L, "result" );
>
> }
>
> So the query of the global result is always execute after running the chunk.
> In my example it was:
>
> ...
> lua_pushvalue(L, -1);
> lua_pcall( L, 0, 0, 0 );
> lua_getglobal( L, "result" );
> ...
> lua_pushvalue(L, -1);
> lua_pcall( L, 0, 0, 0 );
> lua_getglobal( L, "result" );
>
> In this case the output is just again:
>
> l_counter()
> 0
>
> Does the call lua_getglobal(L, "result") also some stack cleaning?
>
> Thanks again and best regards
>
> Joachim
>
> On Saturday 21 August 2010 22:28, Duncan Cross wrote:
>> On Sat, Aug 21, 2010 at 9:17 PM, Joachim Buermann <jbuermann@iftools.com>
> wrote:
>> >    if( luaL_loadstring( L, "result=counter()" ) != 0 ) {
>> >
>> >           std::cout << "Error" << std::endl;
>> >
>> >    }
>> >
>> >    lua_pcall( L, 0, 0, 0 );
>> >
>> >    lua_pcall( L, 0, 0, 0 );
>> >
>> >    lua_getglobal( L, "result" );
>>
>> As well as running the compiled chunk, lua_pcall() removes it from the
>> stack, so the second call will not be trying to run the same compiled
>> chunk.
>>
>> To counteract this, try making a copy of the compiled chunk value by
>> using lua_pushvalue(), so the copy is removed instead:
>>
>>   lua_pushvalue(L, -1);
>>   lua_pcall(L, 0, 0, 0);
>>   lua_pushvalue(L, -1);
>>   lua_pcall(L, 0, 0, 0);
>>
>> -Duncan
>