Common Runtime Errors

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.

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.

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;
}

Tips to avoid segmentation faults:

• Always initialize pointers before use.
• Check if a pointer is NULL before dereferencing.
• Use array bounds checking.

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.

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;
}

To prevent buffer overflows:

• Use fgets() instead of gets().
• Validate input sizes before writing to arrays.
• Use memory-safe functions like snprintf().

A memory leak occurs when allocated memory is not freed, leading to wasted memory.

Causes:

• Forgetting to use free() after malloc().
• Overwriting a pointer without freeing the old allocation.

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!