This is Part 2 of my Integrating Lua into C++ Tutorial series.

Lua Call C Function Example Excel
Lua Call C Function Example
Lua Call C Function Examples
C++ With Lua
Lua Call C Function Example Python
Lua Call C Function

For this part of the tutorial series, we will be discussing on how to interact with classes and objects, both in Lua and C++.

26 – Calling C from Lua. One of the basic means for extending Lua is for the application to register new C functions into Lua. When we say that Lua can call C functions, this does not mean that Lua can call any C function. (There are packages that allow Lua to call any C function, but they are neither portable nor robust.). Introduction; Anatomy of a Lua to C Call; Putting It All Together; Make an msleep Function; We've Just Scratched the Surface; Introduction Earlier you read the Calling Lua From a C Program web page showing how to call Lua from C. There are a lot of instructions with no examples, always leaving something out, so you have to keep trying various things by trial and error, and there. C# (CSharp) NLua Lua.GetFunction - 13 examples found. These are the top rated real world C# (CSharp) examples of NLua.Lua.GetFunction extracted from open source projects. You can rate examples to help us improve the quality of examples. Since the Lua script in this tutorial only defines a function, calling luaLdofile simply makes the function available to our program. As I said earlier, functions in Lua can accept multiple arguments and return multiple results. This is done using a stack. To call a Lua funcion, we first push the function onto the stack. The function is.

Using a C++ class in Lua

First off, let’s bind a simple C++ class so that we can use the class in our lua code. You can name your class anything, but I’m going to use something simple, ‘CppObject’.

Create a class with the following interface and implementation:

CppObject.hpp

This is a simple c++ class with a function that prints out “Test1Function1 Called!” when called.

This code helps to bind the C++ object into a Lua object with the alias ‘CppObject.

Lets dissect the code line by line.

state.new_usertype<CppObject>('CppObject', 'TestFunction1', &CppObject::TestFunction1);

This line defines the new Lua Usertype and also defines the member function ‘TestFunction1’ to specify that the class contains this function.

state.do_string('cppObj = CppObject:new() cppObj:TestFunction1()');

In this line, we create a new object ‘cppObj’ of type ‘CppObject’ and invoked it’s member function.

If all goes well, you should printed:

TestFunction1 Called!

Congratulations! You now know how to play around with C++ Objects in your lua code. If you are really interested in learning more about this, The tutorials over in the Sol2 github page really covers this extensively.

Using a Lua class in Lua

Before we go over using a Lua class in C++, let’s first do it in Lua.

The Lua language does not have any implementation of classes but they do have something called metatable that allows you to do really cool stuffs. One of them is to implement a class system. For this, we will be using a library called middleclass. Middleclass is an OOP library that I really like to use. It’s very lightweight, and easy to use.

I will only be covering the basics, so head over to their github page for more info.

For starters, download the middleclass file and then add it into your scripts folder. I’ll show you how to set it up later.

For now, go to your scripts folder and create a new lua file with the following code:

TestClass.lua

The code above defines the class that we will be using, ‘TestClass’.

The initialize function will be called whenever a TestClass object is created. You can say that it’s the constructor of the class.

state['package']['path'] = (package_path + ';scripts/middleclass.lua').c_str();

Here, I initialized the middleclass library by adding it into the luastate”s package path.

state.do_file('scripts/TestClass.lua');

I then ran the ‘TestClass.lua’ file that defines my TestClass Lua class.

state.do_string('testObj = TestClass:new() testObj.TestFunctionCall()');

I then created a TestClass object and called it’s member function ‘TestFunctionCall’

If everything went well, you should be printing this on the console:

TestClass Created!
TestClass TestFunction Called!

This is just a basic functionality for using MiddleClass together with Sol2. I hope you find it useful.

Using a Lua class in C++

Now we get to the more interesting part of the tutorial, using a lua object in c++. I find that the best way for this is to create a wrapper class.

You actually do not need to create a wrapper class like ScriptObject as you can just save it into a sol::table but I would recommend making one to make your life easier.

ScriptObject.hpp

Whew this is rather long. This class omits out quite a few functions for it to be usable, but it contains the bare-bones of what we need for the tutorial. I wanted to keep it simple. Don’t worry though, I’ll share the full class implementation later.

This is the non-default constructor of the ScriptObject.

This function creates a Lua object of type ‘luaClassName’ and gives them a unique name for use in the luaState. The name is then saved in m_scriptVarName.

m_luaObjectData = (*m_pLuaState)[m_scriptVarName];

If you remember the previous tutorial, then this should be rather familiar. Here, we save the lua object into m_luaObjectData for easy access.

m_pLuaState->script(luaScript, [&isValidCreation](lua_State* state, sol::protected_function_result res) { isValidCreation = false; return res; });

The most complex part about this function would most probably be in this line. I created this lambda function to suppress an exception being thrown if the lua code called is not valid. In this case, it would usually be called if the Lua-class of the object you are trying to create is not valid.

If an exception is thrown, we will set isValidCreation to false, and then stop with the creation of the object.

If m_initialized boolean is set to true at the end of the function, it would mean that your object is successfully created.

This helper function helps us call the lua object’s member functions.

In the destructor, we set the object to nil and then let the garbage collection do all the work.

Alright, so we have already defined our ScriptObject wrapper class. So now let’s try using it.

So here we create our ScriptObject object and then call the “TestFunctionCall” function. The behaviour is totally the same as the previous example.

Lua Call C Function Example Excel

If everything went well, same as before, you should be printing this on the console:

TestClass Created!
TestClass TestFunction Called!

Lua Call C Function Example

Summary

This part of the tutorial is where you start having the basic knowledge on OOP on Lua, as well as handling classes in both Lua and C++ codes.

Lua Call C Function Examples

Codes

CppObject.hpp

C++ With Lua

ScriptObject.hpp

Lua Call C Function Example Python

ScriptObject.cpp

Main.cpp

Lua Call C Function

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