Скачать или смотреть How to Retrieve the Line Number of a Lua Table from its Address

Learn how to easily access the line number of a Lua table by utilizing a helper function, even if you only have the table's address.
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This video is based on the question https://stackoverflow.com/q/65463286/ asked by the user 'user9568523' ( https://stackoverflow.com/u/9568523/ ) and on the answer https://stackoverflow.com/a/65465287/ provided by the user 'Alexander Mashin' ( https://stackoverflow.com/u/6632736/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

As a Lua programmer, you might occasionally find yourself needing to access the exact line number where a table was defined—especially if you're debugging or logging information. However, there isn't a direct way to retrieve the line number just from the table's address. Fortunately, there's a method to achieve this using Lua's debugging functions in conjunction with a helper function.

In this guide, we'll explore how to create a solution that allows you to retrieve the line number of a Lua table while having its reference, all within the context of Lua version 5.1.

Problem Overview

Imagine you have two tables, a and b, which are initialized like so:

[[See Video to Reveal this Text or Code Snippet]]

If you print these tables, you’ll only see their addresses, like table: 002411A0 and table: 005BC470. Now, the question arises:

How can I get the output showing the line number where these tables are defined, such as a.lua:1 in table a or a.lua:2 in table b, when I only have the table's address?

This scenario is common, and you might wonder if you need to dig into Lua's source code or compiled files to accomplish this. Thankfully, the answer is no!

Solution: Creating a Logger Function

To bridge the gap between the table address and the line number, we can create a helper function called logged. This function will enhance your table with a field to store the line number during its creation.

Step-by-Step Implementation

Step 1: Define the logged function

This function will accept a table as its argument and use Lua's debug library to fetch the current line number:

[[See Video to Reveal this Text or Code Snippet]]

In this function:

debug.getinfo(2).currentline retrieves the line number of the line where the table is created.

A metatable is assigned, allowing us to define custom indexing behavior with __index, which enables access to the __line field.

Step 2: Create your tables using the logged function

Now, whenever you initialize your tables, use the logged function:

[[See Video to Reveal this Text or Code Snippet]]

Expected Output

When you run the above code, you'll see outputs reflecting the line numbers based on your code setup:

For table a: It might show 12 (line number)

For table b: It may show 14 (line number)

This way, you've successfully associated each table with the line number where it was defined.

Conclusion

Utilizing the Lua debug library along with a custom logger function allows you to easily retrieve the line number of a table from its address. This approach enhances your debugging capabilities and promotes a clearer understanding of your code structure.

If you're delving into Lua programming, especially on version 5.1, consider implementing this solution to enrich your development experience!