COMP XXXXXXXXXXTutorial 5 Specification
COMP 2401 − "Introduction to Systems Programming"
Tutorial 5 - Managing Memory
Tutorial 5
Managing Memory
Learning Objectives
After this tutorial, you will be able to:
● Use dynamic memory when writing C programs. Specifically:
○ Allocate Memory
○ Pass Parameters by Reference
○ Free Memory No Longer Needed
● Use valgrind to debug memory leaks
Tutorial
In order to receive full marks, you must complete everything in the “Tutorial” section. Part marks may be provided if
good progress was made toward completing the tutorial, at TA discretion.
1. Download the file T05.tgz from the tutorial module on Brightspace. Untar and read through the files.
Rather than tar a file (making a .tar file) and then gzip it (making a .tar.gz file), you can create one file (a
.tgz file) that does both! You can extract the files in a .tgz file with an appropriate option using tar.
2. Compile the program with the -g flag to include debugging information; this is helpful when using valgrind.
gcc -Wall -std=c99 -o t05 t05.c t05util.c -g
Note that in this tutorial, we are compiling two source files. What happens if we only compile t05.c?
We will be covering more ways of compiling multiple files shortly, but you can just follow along for now!
3. Run valgrind on the executable output t05 to check for memory leaks:
valgrind ./t05
4. Fix t05.c to remove the memory leaks.
When you run valgrind without any options, you will notice that it gives a nice summary of the state of the memory
at exit, but if there are leaks, it will recommend that you rerun valgrind with the --leak-check=full option.
Try that out, and carefully read the output to see if it helps you to hunt down your memory leaks.
Note: calloc(1, size) is like malloc(size) in that they both reserve a single “size” of space, but calloc() will make
sure the memory that is allocated is all zeroes so that we don’t accidentally read ga
age data. It is beneficial if
we can’t guarantee that all of our memory will be properly initialized, as we can then check whether it’s initialized
or not.
5. Implement the functions growA
ay() and addStudent() as prototyped. If addStudent() is called and the
a
ay is full, use growA
ay() to increase the a
ay’s capacity before adding the student.
Hint: The “a
ay” in StudentA
ay is a pointer to a dynamically allocated block of memory! Is there any reason we
couldn’t point it to a large, newly allocated block?
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COMP 2401 − "Introduction to Systems Programming"
Tutorial 5 - Managing Memory
6. Use valgrind to ensure that the changed program has no memory leaks.
Exercises
These exercises are optional, but are provided to give you some additional practice working with common operations that
you will encounter while using pointers that might be tricky when you first work with them.
1. Write a function removeStudent(StudentA
ay* stuA
ay, int index) which removes the student at
the given index.
What impact does the removal have on stuA
ay->count? Make the necessary changes to stuA
ay so that
printA
ay() still functions co
ectly after removal.
2. Alter the function addStudent() so that stuA
ay will always be sorted alphabetically by name.
Saving and Submission
In-Person Attendance: Submission is optional, as you can be checked off in class, but you must still complete the
equired portion of the tutorial for marks.
Asynchronous: If you are completing the work on your own at home, make sure to follow the submission requirements.
1. Create an archive to submit your files, and include all of the files that you worked with in the tutorial.
a. They may be submitted as a .tar, .tar.gz, or .tgz file
. Make sure to include all of the code needed to run your program
2. For full marks you should have completed all problems in the Tutorial section (and they should be seen upon
unning the program) without any memory leaks on exit. The exercises are optional, but highly recommended fo
the extra challenge and exploration of these concepts.
3. For part-marks you should have attempted to complete most of the tutorial. Grades for part-marks will be at TA
discretion.
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