Understanding String Reversal in C++: Reverse String Using Pointer Arithmetic

Описание: Dive deep into how to reverse a string in C++ using pointer arithmetic with an example function. This guide provides a clear breakdown and explanation of the entire process.
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This video is based on the question https://stackoverflow.com/q/69520116/ asked by the user 'yurachika2020' ( https://stackoverflow.com/u/11105501/ ) and on the answer https://stackoverflow.com/a/69520143/ provided by the user 'axby' ( https://stackoverflow.com/u/9596600/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding String Reversal in C++: Reverse String Using Pointer Arithmetic

Reversing a string is a common programming task, and in C++, it can be accomplished using pointer arithmetic. If you're diving into C++ string manipulation, understanding how to utilize pointers effectively is essential. This guide will explore a specific example of reversing a string using pointer arithmetic, breaking down the code step by step to clarify each part of the process.

The Problem

You may have come across a scenario where you wanted to reverse a string in C++. The provided code snippet showcases a function called reverseString that uses pointer arithmetic to achieve this. If you're struggling to grasp how it works, don't worry! We'll dissect the function together and outline the logic behind each line.

The Function Breakdown

Here’s the full function again for reference:

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Let's break it down into clear sections for better understanding.

Step 1: Calculating String Length

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This line calculates the length of the input string str using the strlen function. This value is important as it helps in memory allocation for the new reversed string.

Step 2: Memory Allocation

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Here, we dynamically allocate memory for a new string that is one character longer than str to account for the null terminator (\0). The pointer result points to the start of this newly allocated memory.

Step 3: Setting the Pointer for the End of the String

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This line positions another pointer, res, at the end of the allocated memory which is initially len characters after result. This will eventually be where we start placing the reversed characters.

Step 4: Adding the Null Terminator

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In this step:

We place the null terminator at the end of our new string by dereferencing res.

After placing the null terminator, we decrement res so that it points to the last character that will be added to the reversed string.

Step 5: Reversing the String

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The loop runs until we reach the end of the input string (str). Here's what happens during each iteration:

The character pointed to by str is copied to the location pointed to by res.

We then decrement res to move to the previous character location in the result string.

Simultaneously, we increment str to move to the next character in the original string.

Step 6: Returning the Result

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Finally, we return result, which points to the beginning of the new string containing the reversed version of the original input string. This is crucial because returning res would direct us to the null terminator, rather than the start of the new string.

Conclusion

By following this step-by-step approach, you should now have a clearer understanding of how to reverse a string in C++ using pointer arithmetic. This method not only teaches you about string manipulation but also about the power of pointers in C/C++. Practice this function and modify it further to solidify your learning! Happy coding!