Accessing result Field from Arrays of Structs in Multithreaded C Programs

This guide guides you through resolving issues when accessing result fields in arrays of structures during multithreading in C programming. --- This video is based on the question https://stackoverflow.com/q/64698525/ asked by the user 'bobbyrne01' ( https://stackoverflow.com/u/595833/ ) and on the answer https://stackoverflow.com/a/64699211/ provided by the user 'bobbyrne01' ( https://stackoverflow.com/u/595833/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Accessing result field from array elements of structs after thread has completed execution Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Understanding Multithreading in C: Accessing Result Fields from Structs Programming with threads can introduce complexities, especially when it comes to managing data across those threads. If you’re writing a C program to calculate the average of a series of numbers using multiple threads, you might encounter some tricky errors. In this post, we’ll delve into a common problem: accessing the result field from an array of structs after threads have completed execution. We'll also guide you through a solution that resolves this issue effectively. The Problem Imagine you have a program that aims to calculate the average of twelve floating-point numbers by dividing the work among six threads. Each thread is responsible for adding two numbers together and storing the result in a structure. However, when trying to access the results after thread execution, an error occurs: [[See Video to Reveal this Text or Code Snippet]] This error can be confusing, especially if you’re accustomed to using pointers in C. Let's explore the details of the solution and how to resolve this error line. Struct and Its Purpose In our program, we define a struct named args to store the numbers and their computed result. Here’s what it looks like: [[See Video to Reveal this Text or Code Snippet]] The result field is intended to hold the sum of firstNumber and secondNumber calculated in each thread. The Solution: Correcting the Access Method The issue arises from the way we are trying to access the result field within the array of struct args. To fix it, we should follow these steps: Use the Dot Operator Instead of the Arrow Operator: Since subsetsOfNumbers[thread] refers to an instance of struct args and not a pointer, you need to access its members using the dot (.) operator instead of the arrow (->) operator: Change this line: [[See Video to Reveal this Text or Code Snippet]] To this: [[See Video to Reveal this Text or Code Snippet]] Ensure Incorrect Symbols are Not Present: Sometimes, complications such as duplicate symbol errors can arise if the function that is attempting to access a struct member is declared in a different file. Always keep your declarations organized and make sure that conflicting names are avoided. Implementing the Fix After making the above changes, your code snippet where you calculate totalSum would look like this: [[See Video to Reveal this Text or Code Snippet]] With this change, you should be able to compile and run your program without running into the initial error. Conclusion Multithreading in C can be a powerful way to perform tasks simultaneously, but it can also lead to tricky errors if not handled properly. The key takeaway here is to ensure that you correctly reference struct members using the appropriate access operator based on whether you're dealing with a struct or a pointer to a struct. By following the guidance provided above, you should have a clearer understanding of how to access results from structs in multithreaded environments. Happy coding!