CS2110 Homework 9 Dynamic Memory Solution

1.1 Purpose
The purpose of this assignment is to introduce you to dynamic memory allocation in C. You will also learn how to implement a singly-linked list data structure in C.
How do we allocate memory on the heap? How do we de-allocate it when it is no longer used?
1.2 Task
In this assignment, you will be implementing a singly-linked list data structure. Your linked list nodes will have struct data (of type struct student*). You can find details about this struct and the fields it contains in the included list.h file. Your linked list will be able to add, remove, and mutate, and query the data stored within it. You will be writing code in
1. list.c
2. main.c
The main.c file is included only for your own testing purposes.
1.3 Criteria
You will be graded on your ability to implement the linked list data structure properly. Your implementation must be as described by each function’s documentation. Your code must manage memory correctly, meaning it must be free of memory leaks.
Note: A memory leak is when a block of memory is allocated for some purpose, and never de-allocated before the program loses all references to that block of memory.
2 Instructions
2.1 Implementation Overview
You have been given one C file, list.c, in which to implement the linked list data structure. Implement all functions in this file. Each function has a block comment that describes its expected behavior.
Be sure not to modify any other files. Doing so will result in point deductions that the autograder will not reflect.
Remember that the struct data passed to certain functions (struct user *data) is malloc-ed data.
Forgetting to free this data when it is removed can cause memory leaks (memory that is no longer being used, but is never freed). Freeing memory when it should be returned to the user can created dangling pointers (memory that’s freed but still being referenced), causing use-after-free bugs. Keep both of these in mind when writing your code.
You are given a struct user_list, which is a linked list with a head pointer that points to the first node in the list and a size which represents the length of the linked list. You also have a struct user that has a next pointer to the next user as well as a union user_data pointer that points to a memory address with all the data for that user.
Refer to the following example for a visual representation of the data structure, where “...” denotes an unknown pointer address (pointing to some memory allocated on the heap):

Please COMPILE OFTEN. The compiler will reveal many syntax errors that you would rather find early before making them over and over throughout your code. Waiting until the end to compile for the first time will cause big headaches when you are trying to debug code. We speak from experience when we say compile often. :)
2.2 Implementation Tips
• Push/add functions: For these functions, make sure to read the documentation about what to do when malloc fails. In most cases, this means that you need to return 1 to indicate something went wrong.
• Pop/remove functions: As we mentioned, you should free things that are no longer used to avoid memory leak, but you also don’t want to free prematurely. Here, the potential candidates for freeing are: the nodes, the struct user data inside the node, and the pointers inside the struct user. Think carefully about what you’re doing in these functions (hint: look at return type) and figure out what should be freed.
2.3 Testing and Autograding
To compile and test your code, use the provided Makefile as detailed below. All commands should be run from inside of the CS 2110 Docker container.
2.3.1 Manual testing
To manually test specific functions in your code, fill in the main function in main.c with tests and run
$ make hw9
This will create an executable called hw9. Then, you can run your tests via your main function by running
$ ./hw9
2.3.2 Running the Autograder
To run the autograder’s test suite, run:
# Run all test cases $ make run-tests
# Run a specific test case
$ make run-tests TEST=test_list_contains_NULL_name
Note that the above only runs logical tests on your implementation. The local autograder does not test for memory errors by default, though the one on Gradescope does. To test your code for memory errors locally, you must run valgrind.
To check your code for memory errors using valgrind, run:
# Run all test cases $ make run-valgrind
# Run a specific test case
$ make run-valgrind TEST=test_list_pop_front_nonempty
3 Deliverables
Please upload the following files to Gradescope:
1. list.c
4 Appendix
4.1 Rules and Regulations
4.1.1 General Rules
2. If you find any problems with the assignment it would be greatly appreciated if you reported them to the TAs. Announcements will be posted if the assignment changes.
4.1.2 Submission Guidelines
2. You are also responsible for ensuring that what you turned in is what you meant to turn in. After submitting you should be sure to download your submission into a brand new folder and test if it works. No excuses if you submit the wrong files, what you turn in is what we grade. In addition, your assignment must be turned in via Canvas/Gradescope. Under no circumstances whatsoever we will accept any email submission of an assignment. Note: if you were granted an extension, you will still turn in the assignment over Canvas/Gradescope unless instructed otherwise.
4.1.3 Syllabus Excerpt on Academic Misconduct
Academic misconduct is taken very seriously in this class. Quizzes, timed labs and the final examination are individual work.
Homework assignments are collaborative, In addition many if not all homework assignments will be evaluated via demo or code review. During this evaluation, you will be expected to be able to explain every aspect of your submission. Homework assignments will also be examined using computer programs to find evidence of unauthorized collaboration.
You are expressly forbidden to supply a copy of your homework to another student via electronic means. This includes simply e-mailing it to them so they can look at it. If you supply an electronic copy of your homework to another student and they are charged with copying, you will also be charged. This includes storing your code on any site which would allow other parties to obtain your code such as but not limited to public repositories (Github), pastebin, etc. If you would like to use version control, use github.gatech.edu
4.1.4 Is collaboration allowed?
What you shouldn’t be doing, however, is pair programming where you collaborate with each other on a single instance of the code. Furthermore, sending an electronic copy of your homework to another student for them to look at and figure out what is wrong with their code is not an acceptable way to help them, because it is frequently the case that the recipient will simply modify the code and submit it as their own.