Скачать или смотреть How to Detect the Struct a Function is Called From in C

Learn how to effectively manage function behaviors in C by associating them with structs, enhancing your programming logic and structure with practical examples.
---
This video is based on the question https://stackoverflow.com/q/74788228/ asked by the user 'DominicusPurple' ( https://stackoverflow.com/u/20492895/ ) and on the answer https://stackoverflow.com/a/74788489/ provided by the user 'Ted Lyngmo' ( https://stackoverflow.com/u/7582247/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: how to detect what struct a function is being called from

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Detect the Struct a Function is Called From in C: A Comprehensive Guide

When working in C, it can be tricky to handle functions that need to act on specific instances of structs. One common challenge among programmers is determining which instance of a struct a given function is being called from. This post aims to clarify this concept and provide a structured approach to solving it effectively.

The Problem Explained

Imagine you have a struct named Object that contains a boolean variable _active and a function SetActive(). You want to be able to call SetActive() on an instance of this struct while ensuring that it modifies the appropriate _active variable for that specific instance. In simpler terms, if you call structname.SetActive(true), you need to update structname._active, but how can you manage this relationship given that C does not support member functions like higher-level programming languages?

Understanding C Function Pointers

The root of the confusion often lies in misunderstanding how function pointers work in C. In your original approach, the declaration void (*SetActive)(bool); represents a pointer to a standalone function rather than a method tied to a specific instance of a struct. This means the function lacks a direct connection to the struct that it's intended to modify.

To maintain clarity and establish the connection to a specific instance, you can adopt a different approach by passing a reference to the struct as an argument to the function that you want to behave like a member function.

A Structured Solution

Step 1: Define the Struct

First, we will define the struct Object with a boolean variable _active. This struct will serve as a blueprint for creating Object instances that you can manipulate throughout your program.

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

Step 2: Implement Object Creation and Destruction

Next, we'll create functions to initialize and free our struct instances. This is essential for managing memory effectively and avoiding leaks.

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

Step 3: Create the SetActive Function

Instead of attempting to make a pointer function that ties directly to the struct, we'll refactor SetActive to accept a pointer to an Object. This way, you can easily modify the _active state of the respective struct instance.

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

Step 4: Utilizing Your Functions

Now, let's put everything together in the main function. You'll create an instance of Object, use the Object_SetActive function to modify its _active state, and then clean up the allocated memory afterward.

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

Conclusion

By following the structured approach outlined in this post, you can effectively create functions in C that operate on specific instances of structs. This results in cleaner, more organized code and eliminates confusion around function behavior. Remember, clear relationships between structs and functions not only enhance readability but also pave the way for more maintainable code in the long run.

Takeaway: Always pass the struct instance as an argument to functions that need to modify it!