Library for binding C code with Lua. Contribute to aphenriques/integral development by creating an account on GitHub. The Lua C api allows C programmers to manipulate values on the Lua stack. This is incompatible with Ravi’s type-checking because the compiler doesn’t know about these operations; hence if you need to do such operations from C code, please ensure that values retain their types, or else just write plain Lua code. When the above code is compiled together and executed, it produces the following result − Average value is: 214.400000 As you can see, the length of the array doesn't matter as far as the function is concerned because C performs no bounds checking for formal parameters.

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Recently, I was using Lua [1] in one of my projects. I got stuck in a trivial problem. The project which was written in Lua, was generating a massive amount of data. My aim was to save this data in files in approximately real-time. Fortunately, I was able to decompose the data into 1-dimensional arrays (table).

To get anything from an array, the script needs to know the location of that value in the array. Whenever a value is added to an array, it’s assigned a number called an index. In Lua, Indexes start at one, and go up by one for every value added. In this example, 'Hi' is at index 1 and 'Good bye!'

In this post, I am going to explain an efficient way of dumping large Lua 1D arrays into files. We are going to use Userdata provided by Lua [2]. The userdata offers a raw memory area with no predefined operations. Note that once we have access to raw memory, we can do operations quickly. We are going to use Lua C bindings [3] for this purpose.

Let’s code. First, we need to define the following structure to hold the data. In our case, we are dealing with float type data.

Let’s define a function to create an array using userdata-

The above function expects an int https://newrex.amebaownd.com/posts/18912700. number to define the size of this array. Now we need a way to set each element of this array. Let’s define a function for the same as shown below-

We should also define other helper functions to get the element and size from this array.

At this stage, we need a function which can dump this array into a file. In the following function, I am going to write a binary file containing float values. since userdata provides raw memory access, we can use fwrite function [4] provided by stdio.h in C language to write a block of memory into the file. Below is the function- Garminfone unlock code free.

We are almost done. Now, we can create an array in Lua and then we can set each element of this array. Finally, we can dump this array to a file as well. BUT wait!!! can we improve it more? Yes, we can! Instead of setting each element of this array in Lua, what if we can provide a 1d array to C function and it sets each element inside C? It sounds great. Isn’t it? Let’s do it.

We are going to provide a 1d array to the function defined as shown below-

Notice carefully that first, we created userdata, and then we filled each element. This is much quicker than filling the elements in Lua. Once we have the array, we can dump it as shown previously using fwrite.

At this point, you may be wondering that why are we creating an array first and then dumping it in later stages. It clearly gives you more freedom, such as you can easily change the elements of this newly created array, etc. Before finishing our Lua C binding, I would like to add one more function, which doesn’t create an array as shown below-

C++ Array To Lua Code Translator

Can you find out the difference? Instead of creating userdata, we created a float array here. Let’s add few more functions and finish this binding-

C++ To Lua Converter

This is how we register our functions to Lua-

Note carefully, that using switch statements we have encapsulated the complexity associated with array creation and array dumping operations beautifully.

Compilation

Before proceding further make sure to download the code from the repository [6].

Open terminal or press CTRL+ALT+T
Compile C code using the following command-
The above command is going to produce shared object.

Usage

We can use the above shared object in Lua code as shown below-

Environmental Details

Ubuntu 14.04 LTS 64 Bit OS
Lua v5.1
GCC v4.8.4

Install Lua v5.1

Open terminal or press CTRL+ALT+T then use following command-
Install Lua headers by following command-

Benchmarking

In order to benchmark our binding, we should use the standard Lua I/O libraries to write a file. We are going to measure the elapsed time in Lua [5].

Below are the results of benchmarking-

Case	Elapsed time (second)
Direct dump	0.0343
Create array then dump	0.0367
Standard Lua I/O	3.1897

Convert Lua To C

Clearly, we can see a huge difference in elapsed time while using Lua userdata. All the code is available to download from the repository [6].