Common pointer errors - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens if you dereference a NULL pointer in C?

Dereferencing a NULL pointer causes a runtime error called a segmentation fault, which usually crashes the program.

beginner

Why is using an uninitialized pointer dangerous?

An uninitialized pointer points to an unknown memory location, so dereferencing it can cause unpredictable behavior or crashes.

intermediate

What is a dangling pointer?

A dangling pointer points to memory that has already been freed or released, so using it can cause errors or corrupt data.

intermediate

What is the risk of pointer arithmetic errors?

Pointer arithmetic errors can cause pointers to point outside the intended memory area, leading to invalid memory access and program crashes.

intermediate

Why should you avoid freeing the same pointer twice?

Freeing the same pointer twice (double free) can corrupt the memory management system and cause crashes or security issues.

What does a NULL pointer represent in C?

A A pointer that points to no valid memory

B A pointer to the first element of an array

C A pointer to a freed memory block

D A pointer that points to a random memory location

A NULL pointer explicitly means it points to no valid memory location.

What is the main problem with using an uninitialized pointer?

A It always points to NULL

B It points to a random memory location

C It points to a valid variable

D It automatically allocates memory

Uninitialized pointers contain garbage values and can point anywhere, causing unsafe behavior.

What error can occur if you dereference a dangling pointer?

A Memory allocation success

B Compilation error

C Segmentation fault or undefined behavior

D No error, safe to use

Dangling pointers point to freed memory, so dereferencing them causes crashes or undefined behavior.

What is a double free error?

A Freeing the same memory twice

B Freeing two different pointers

C Not freeing allocated memory

D Freeing a NULL pointer

Double free means calling free() on the same pointer more than once, which corrupts memory management.

Pointer arithmetic can cause errors if:

A Pointer points to a local variable

B Pointer is set to NULL

C Pointer is initialized properly

D Pointer goes outside the allocated memory bounds

Moving pointers outside their allocated memory can cause invalid access and crashes.

Explain what a dangling pointer is and why it is dangerous.

Think about what happens after you free memory but still keep the pointer.

List common pointer errors in C and how to avoid them.

Consider initialization, freeing memory, and careful pointer use.