Скачать или смотреть Understanding the free(): double free detected in tcache 2 Error in C+ +

Discover the causes of the `free(): double free detected in tcache 2` error in C+ + , and find solutions to avoid memory management pitfalls in your coding practice.
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This video is based on the question https://stackoverflow.com/q/68138668/ asked by the user 'Zeor137' ( https://stackoverflow.com/u/3314644/ ) and on the answer https://stackoverflow.com/a/68140213/ provided by the user 'HDMP' ( https://stackoverflow.com/u/11308899/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the free(): double free detected in tcache 2 Error in C+ +

When working with C+ + , you might encounter complex issues related to memory management, particularly when using pointers and dynamic memory allocation. One such error that can be quite confusing, particularly for those new to C+ + or learning through online courses, is the free(): double free detected in tcache 2 error. Let’s unpack this issue in detail and explore how to solve it.

The Problem: A Closer Look at the Error

In scenarios where you dynamically allocate memory using new, it's crucial to ensure that the memory is correctly deallocated using delete. Failing to manage this process properly can lead to memory leaks or, as in our case, attempts to free memory that has already been released.

What Does the Error Mean?

The error free(): double free detected in tcache 2 usually indicates that your code is trying to delete the same memory location more than once. This can lead to undefined behavior, crashes, and hard-to-diagnose bugs in your C+ + programs.

Analyzing the Example Code

Let’s consider the provided code snippet to identify where the mistake happens:

Code Breakdown

Here's a simplified version of your class structure and main function:

Struct Definitions:

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

Line Creation:

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

Deep Copy Implementation:

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

What Happens During Execution?

You create three Line objects in total during execution:

line in main

copy in main

copy in deep_copy (static)

Destruction Phases:

The destructor for main::copy gets called first, which deallocates start and end.

Next, the destructor for main::line is called, also deallocating start and end.

Finally, the destructor for deep_copy::copy is executed. However, since deep_copy::copy shares the same memory locations (because it was a shallow copy of the pointers), it attempts to free already freed memory.

The Solution: Fixing Memory Management

Correcting the Deep Copy Method

To prevent this double freeing of memory, we can modify the deep_copy method to ensure that a true copy of the original pointers is created:

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

Avoid Static Local Static Objects

Avoid using static objects in the deep_copy() function as this leads to potential scope-duration issues that complicate memory management. Instead, returning a Line object directly allows for better control:

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

By returning local objects created with new, you ensure that each Line object manages its pointers safely.

Conclusion

Memory management in C+ + requires careful attention to detail, especially when using dynamic memory allocation. The free(): double free detected in tcache 2 error serves as a reminder of the complexities involved. Make sure to implement proper copy semantics and always handle pointers responsibly. By following these guidelines, you can avoid common pitfalls and enhance the stability of your C+ + applications.

By addressing memory leak issues and ensuring that destructors behave as expected, you can create more robust software solutions.