Common Runtime Errors
Identify and prevent segmentation faults, buffer overflows, and memory leaks.
Common Runtime Errors is a free C Academy lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
1
Common Runtime Errors in C
Runtime errors occur when a program runs into unexpected behavior, often causing crashes.
In this lesson, you will learn:
- How segmentation faults occur and how to fix them.
- How buffer overflows lead to security vulnerabilities.
- How memory leaks affect performance and how to avoid them.
2
What is a Segmentation Fault?
A segmentation fault occurs when a program tries to access memory it is not allowed to.
Causes:
- Dereferencing an uninitialized or NULL pointer.
- Accessing memory beyond array bounds.
- Modifying read-only memory.
3
Example: Segmentation Fault
This program causes a segmentation fault by dereferencing a NULL pointer.
#include <stdio.h>
int main() {
int *ptr = NULL;
printf("%d\n", *ptr); // Segmentation fault
return 0;
}4
Preventing Segmentation Faults
Tips to avoid segmentation faults:
- Always initialize pointers before use.
- Check if a pointer is NULL before dereferencing.
- Use array bounds checking.
5
What is a Buffer Overflow?
A buffer overflow occurs when data exceeds the allocated memory space.
Example:
char arr[5]; gets(arr);
This can lead to unpredictable behavior and security vulnerabilities.
6
Example: Buffer Overflow
This program demonstrates a buffer overflow using gets().
#include <stdio.h>
int main() {
char buffer[5];
printf("Enter a string: ");
gets(buffer); // Unsafe, may cause buffer overflow
printf("You entered: %s\n", buffer);
return 0;
}7
Preventing Buffer Overflows
To prevent buffer overflows:
- Use
fgets()instead ofgets(). - Validate input sizes before writing to arrays.
- Use memory-safe functions like
snprintf().
8
9
Memory Leaks
A memory leak occurs when allocated memory is not freed, leading to wasted memory.
Causes:
- Forgetting to use
free()aftermalloc(). - Overwriting a pointer without freeing the old allocation.
10
Summary
In this lesson, you learned:
- How segmentation faults occur and how to prevent them.
- How buffer overflows lead to security issues.
- How memory leaks waste system resources.
Next, we will explore exception handling strategies in C!
Frequently asked questions
Is the “Common Runtime Errors” lesson free?
Yes — the full text of “Common Runtime Errors” is free to read here on the web, and the C Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C Academy course, upgrade to CoddyKit PRO.
What will I learn in “Common Runtime Errors”?
Identify and prevent segmentation faults, buffer overflows, and memory leaks. You practise C Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start C Academy?
No prior experience is required. C Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Common Runtime Errors” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this C Academy lesson?
Yes. Every C Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Debugging with GDB
- Common Runtime Errors
- Exception Handling in C