EDIT: Part 2

Jul 28, 2018 Find out why Close. Embedding Lua in C #31 - Handling User Values Using Run Time Type Information. Some knowledge of the Lua scripting langage itself is preferable as this is not a scripting.

If by unload you mean undo the effects of running some Lua code, then it cannot be done unless you save the state of what is precious before running the code. This can be done by sandboxing the code. If you just want to remove a Lua table, set to nil all references to it and let the table be garbage collected automatically or manually. They must be defined as extern 'C' because Lua is compiled as a C library and it will call all the luaCFunction with a C linkage (that determines the order in which the function parameters will be pushed into the machine’s stack, etc.) so we need to make sure that the function that we are generating here can be called from C. Then, the function will need to be registered with lua. Step 1: Writing a C function that Lua can call. C/C functions that are called from lua need to take as an input parameter the lua state. The parameters can be examined on the call stack using the functions luatointeger, luatonumber, etc (described above). Luaclose -0, +0, – void luaclose (luaState.L); Close all active to-be-closed variables in the main thread, release all objects in the given Lua state (calling the corresponding garbage-collection metamethods, if any), and frees all dynamic memory used by this state.

C++ Will A Lua Script Close Itself Using

Long time without posting, busy at work, family, etc.

Today I decided to write a bit on Lua and how to integrate it with C++.

Lua is a scripting language with an emphasis on being easily embeddable. Lua isused as the scripting language in Photoshop CS, and World of Warcraft, forexample. So if you are looking into adding scriptability to your C or C++applications Lua is quite suited for the task.

In order to learn Lua (both the language itself and how to embed it into yourapp) I recommend you Programming in Luaby one of the Luaauthors.

You can find tons of tutorials on how to get started with Lua. So I will focushere on how to integrate with C++. Most of the sources I’ve found about Lua -C++ integrations take the approach of frameworks to automatically wrap yourobjects/classes to be usable from within Lua. I find this approach confusing, Ithink it’s better to learn how to do it manually, and that’s what I will dohere.

Step 0. Compile Lua itself

Download Lua 5.2.1 and compile it. Usually it enough with make macosx ormake linux. That will generate liblua.a, the library that we will link to.

Step 1. Create a simple host app

We need a simple host app. Our host app will simply setup Lua and run a scriptfrom it. This script will have access to a std::queue from the host app. Thiswill illustrate how you can share objects with the Lua part. Later we will takea more complex example.

Let’s start with the basic skeleton of a lua environment with somecommunication with its host:

The Makefile

It uses LUAHOME that should point to the directory containing both liblua.a and the lua*.h files.

The samplehost application

The Lua script

The code explained step by step:

Initialization

That creates a lua_State loads the standard libs in it and also loads the code in luascript.lua.

Adding variables from C++ into Lua

Then it sets a global variable in Lua from C++ code using lua_setglobal. Ifyou don’t know what are the lua_pushxxxx and the Lua stack, etc. I recomentthat you take a look at the Lua Reference Manual and Programming in Lua.More or less Lua and the C++ communicate through the stack that livesin lua_State and there is bunch of function to manipulate that stack. So inorder to set a global in Lua from C++ you must push the value into the stackand call lua_setglobal that will pop the value in the stack and assign it tothe identifier provided inside the Lua environment.

After setting the global cppvar it executes the loaded chunk of code (that is in the stack) with lua_pcall. The Lua code is able to read and print the value of cppvar. The lua code will also set a new global luavar that we will access from C++.

Reading a Lua variable from C++

To get luavar from C++, we must first use lua_getglobal that will put the value associated with the identifier into the top of the stack and the lua_tonumber will transform whatever it’s at the top of the stack into a double (well a luaNumber) and then we can use that double in our C++ code to print it. Lua

Calling a Lua function from C++

The example won’t be complete without function calling so that’s the next step.Calling a Lua function from C++ it’s quite easy. Function in Lua are firstclass values, so that means that it’s just a like reading a any other value.lua_getglobal will get the value and put it on the stack and then we push thefunction arguments into the stack and use lua_pcall to call the function(that is the stack). The returned value from the function will be pushed in thestack and that’s were the C++ code will get it, lua_tostring and then it willremove from the stack with lua_pop.

Calling a C++ function from Lua

The other way around it’s more complex. You can’t just call any function fromLua. It has to has a special signature lua_CFunction, that is, typedef int(*lua_CFunction) (lua_State *L) a function that returns an int and takes alua_State. This special funciton will communicate with Lua via the lua stackthat resides in the lua_State parameter. The return value of the functiontell lua how many value the function has pushed into the stack as result valuesfor the function call.

So to make the function accesible from Lua, you create push the function intothe stack with lua_pushcfunction and bind it to an identifier in lua withlua_setglobal. Then lua code will be able to invoke this function like anyother function. In the example I call the myfunction (which is lua code) andmyfunction in turn invokes cppfunction which is “bound” to C++l_cppfunction. Ah, I almost forgot. l_cppfunction is declared as extern'C' telling the compiler to provide C linkage for this function so it can becalled from a C library like Lua is.

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Free Lua resources

lua_close will free all resources held by the lua_State L.

Wrap up

I will leave the part on how to wrap C++ class objects inLua for a later post because Idon’t want to make this post too long. Hopefully I’ll post it tomorrow.

« Moving on

#include <rules> »

07 Nov 2010

Lua Script Gta 5

Lua is a very popular scripting language in game development industry. Many games use Lua for various scripting needs (data representation, UI scripting, AI scripting), and some go as far as write the majority of the game in Lua. At CREAT, we used Lua for all of UI scripting, and for AI and other game logic on some projects. And, well, there were times when the game crashed - and the callstack consisted mainly o