CODEWITHSUNDEEP
c++dllmethodslua
MRodrigues
MRodrigues

Reputation: 2025

Lua Wrapper Class - Exposing c++ static methods to Lua through a DLL

I finally got into a problem that I can't find a solution here. I'm using a Lua Wrapper Class found in here http://lua-users.org/wiki/CppConvenientLuaWrapperClass. We've been able to expose a complete API plus more other funcionalities like serial communication and on.

The concept behind this Lua Wrapper is that you expose every method before compiling so when you're running your programm all methods will be added to the Lua Stack and in that way you can execute them. The idea now is to build kind of a Dll in order to complete this process of exposing methods. This way you won't needed to release a version with all exposed methods instead you load them trough multiple dll files.

I've tried to create another table and register other methods in that table, but with that, previous exposed methods stop working.

The other way around I can think of, is to create a dll but in C that contains all desirable methods and load it directly to Lua. But I think the other way would be better.

Have you been able to do something similar ? Am I having some wrong concept?

Thanks

Humm... I really don't want to change our wrapper at this time. I think I could manage to do it, sort of. Instead of adding a new table for the plugin functions, I've added a new sub-table tha will contain the functions names and cClosures to be called from Lua. So at the end we should have:

application.functionName()
application.plugin.functionName()

Even if it work this way it will do fine. Now I wonder how can we reference the lua_settable when exposing the functions to be added to application[plugin][pluginFunction] instead of aplication[pluginFunction]?! This is how the normal functions are exposed:

//mState is a pointer to a Lua_State
lua_pushstring( mState, functionName );

//methodDesc is a pointer to an object that describes the function arguments/returns 
lua_pushlightuserdata( mState, methodDesc );

//exposeMethodProxy is the method that is responsible for conneting lua c-calls to the c-functions
lua_pushcclosure( mState, exposedMethodProxy, 1 );

//mMethodTableIndex is a member variable that contains the index of the table tha hold all exposed functions
lua_settable( mState, mMethodTableIndex );

Any ideas on how I could achieve adding the cclosures not to the main table(at mMethodTableIndex) as mainTable[functionName] but at maintable[plugin][functionNane].?

Upvotes: 1

Views: 1067

Answers (1)

Dmitry Ledentsov
Dmitry Ledentsov

Reputation: 3660

I'm not sure, you're clear on what you want to do. A typical way to extend lua is to write a DLL with a single method that uses the Lua API to register your C++ types and C functions. To conviniently bind C++ functions and classes, you could use LuaBridge. An example of such binding is here: https://github.com/d-led/xerceslua

The header for the DLL of the xerceslua module contains only one function:

#include <lua.hpp>
void register_xerceslua (lua_State* L);

inside the implementation LuaBridge is used to bind to C++:

#include "xerceslua_lib.h"

#include <lua.hpp>
#include <LuaBridge.h>

void register_xerceslua (lua_State* L) {
...
luabridge::getGlobalNamespace(L)
    .beginNamespace("xerces")
    .addVariable("version",&version,false)
...

in Lua you can then access the exposed C++ API:

assert(require 'xerceslua')

local parser=xerces.XercesDOMParser()
parser:loadGrammar("Employee.dtd",xerces.GrammarType.DTDGrammarType)

You can use Lua both as an embedded scripting language, where you can execute lua from within your software, or you could use it as an extensible scripting language, extending it using the method shown above. Both are valid, but you have to consider, what exactly you are trying to do.

Upvotes: 1

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