Скачать или смотреть Resolving the C+ + Class Variable Not Changing After Assignment Issue

Learn how to fix the problem of class variables not reflecting changes after assignment in C+ + . This guide walks you through understanding object assignment in C+ + and provides a solution to ensure values update as expected.
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This video is based on the question https://stackoverflow.com/q/66092516/ asked by the user 'Reza Kiani' ( https://stackoverflow.com/u/3406159/ ) and on the answer https://stackoverflow.com/a/66092657/ provided by the user 'Werner Henze' ( https://stackoverflow.com/u/1023911/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding C+ + Class Variable Assignment Issues

If you've been coding in C+ + , you may have stumbled upon a frustrating issue: a class variable does not seem to change after assignment. This problem often arises when dealing with class inheritance and custom assignment operators. In this post, I'm going to break down the specifics of this issue and guide you through a solution that ensures your class variables behave as expected.

The Problem at Hand

Consider the following scenario: you have two classes, Test and Test2, where one class contains a private member of the other class. You expect that once you modify this member’s value, any subsequent references to it should reflect that change. However, running the program provides unexpected output. Here's the code:

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When you run this code, you expect the output to be:

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But instead, you receive:

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This discrepancy can be traced back to how your assignment operator is implemented.

Solution: Fixing the Assignment Operator

The primary issue lies within the implementation of your operator= for the Test and Test2 classes. Currently, you are creating a temporary object, modifying it, and not actually changing the object that the assignment operator is working on (this).

Correct Implementation

To solve this issue, you need to modify your operator= implementation. Instead of creating a new instance and modifying that, here’s how you should implement it:

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Key Improvements

Direct Modification: The updated operator= directly alters the current object (this) instead of creating a temporary copy.

Return Type: The operator should return a reference to *this (the current instance), allowing for chaining of assignments.

Updated Example

Here's how the updated sections of your classes would look:

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Now, ensure you do the same for the Test2 class if you implement a custom assignment operator there as well.

Conclusion

By correcting the operator= implementation in your classes, you enable proper assignment behavior, allowing the changes you make in one object to be reflected in others that have been assigned from it. This approach not only resolves the issue but also adheres to good practices in C+ + programming by managing object state correctly.

Now that you understand how to address this problem, you can confidently utilize class variables in your C+ + applications. Happy coding!