Скачать или смотреть Fixing the realloc Function in a Dynamic Array of Structs in C

Discover how to resolve common issues with dynamic arrays in C, specifically when using `realloc` with structs. Improve your coding practice with practical tips and an example code rewrite!
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This video is based on the question https://stackoverflow.com/q/63179957/ asked by the user 'David Choi' ( https://stackoverflow.com/u/5551522/ ) and on the answer https://stackoverflow.com/a/63180831/ provided by the user 'kilio' ( https://stackoverflow.com/u/14023949/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing the realloc Function in a Dynamic Array of Structs in C

When working with dynamic arrays in C, you may encounter issues with the realloc function, especially when handling structs. In this post, we will explore a common problem faced while reading data into a dynamic array of structs and fix it using step-by-step explanations.

The Problem

Imagine you are reading student information from a file into a dynamic array of structs (in this case, struct alumno). You expect each record to be stored independently, but upon printing the results, you notice that every entry displays the same name and surname – only the last student's details are stored for all entries.

This issue typically arises from how pointers and memory are managed. In particular, we need to investigate the way names are stored in memory.

Here's a Closer Look at the Symptoms

The dynamic array seems to correctly allocate memory for the number of students.

The struct properly captures the student IDs.

However, all name and surname fields point to the same memory location, leading to similar output across all entries.

Understanding the Cause

The primary cause of this problem lies in the way you are handling pointers for nombre (name) and apellido (surname) within your loop. Both nombre and apellido are being manipulated directly, causing all entries to point to the same location in memory.

When you modify nombre or apellido, you overwrite the content for every student because they are all referencing the same memory space. To solve this problem, you need to make a separate copy of the strings for each student using the strdup function.

The Solution

To ensure that each student’s name and surname are stored independently, modify your code as follows:

Step 1: Use strdup for Deep Copying Strings

In your leerArch function, update how the name and surname are assigned to the struct like this:

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

Step 2: Manage Memory Allocation Properly

Ensure you allocate space for the necessary strings before copying:

Adjust memory allocation for the nombre and apellido before entering your loops to read the strings.

Revised Code Example

Below is a clearer version of the corrected code to read student information:

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

Tip: Using Safe String Handling Functions

If you are still learning C, consider using functions like getline and strsep to simplify string handling. This can lead to cleaner and more manageable code.

Conclusion

Using realloc in combination with proper memory management is crucial when working with dynamic arrays in C. By ensuring that each string is duplicated for each student record, you can resolve the issue of incorrect data display.

It’s essential to test your code thoroughly and understand how memory is allocated and modified within your program. Keep these tips in mind to enhance your coding skills!

Happy coding!