Understanding memmove: Creating Your Own Implementation in C

Learn how to mimic the behaviour of the `memmove` function in C. This guide walks you through issues, solutions, and best practices for memory copying.
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Mimicking memmove's Behaviour in C

When working with memory manipulation in the C programming language, one of the most commonly used functions is memmove. This function is used to copy bytes from one memory location to another, even when the source and destination memory regions overlap. However, implementing your own version of memmove can be challenging. In this post, we'll delve into a common issue related to creating a mimic of memmove, and how to effectively overcome it.

The Problem

You may find yourself wanting to create a function similar to memmove to better understand memory management in C. An attempt might look something like the following:

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While the above code appears correct at first glance, you may encounter several issues, including the inability to increment the array pointer correctly. A common error you might experience is:

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

This error occurs because the array p is being treated as a fixed-size array rather than a pointer, which can lead to confusion while trying to increment it.

The Solution

To resolve this issue, here's an improved version of the ft_memmove function that utilizes a temporary pointer instead of a fixed-size array.

Key Changes Made

Use of a Temporary Pointer: Instead of relying on a fixed-size temporary array, we can declare a pointer to an array and manipulate this pointer to move through our temporary storage.

Correctly Incrementing Pointers: By working with pointers instead of arrays, we can easily increment our position.

Here’s the corrected implementation:

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Explanation

Temporary Storage: The temp array holds the bytes temporarily, allowing overlap between the source and destination safely.

Copying Logic: The first loop copies the data from the src to temp. The second loop then moves this data from temp to dest.

Conclusion

Understanding how memmove works under the hood can enhance your programming skills and deepen your understanding of memory management in C. The solution provided not only fixes the original issues but also illustrates a solid practice for implementing similar functions in the future.

By learning the nuances of pointers and memory in C, you equip yourself with the tools necessary to handle complex data manipulation tasks.

Feel free to try and adapt this function in your own projects and experiment with different scenarios to solidify your understanding!