C Programming Interview Questions Part 28: What is null pointer and what are its typical use cases?

C Programming Interview Questions Part 28: What is a null pointer and what are its typical use cases?

A null pointer is a special pointer value that doesn’t point to any valid memory location. In C, it is represented by NULL (defined in stddef.h or stdio.h), and its value is typically zero.

Dereferencing a null pointer leads to undefined behavior, usually causing a crash. However, null pointers are useful in many scenarios where a pointer needs to signify “no object” or “invalid address.”

Typical use cases:
• Function arguments to indicate optional data.
• Return values from functions to indicate failure (e.g., malloc() returning NULL on failure).
• End of data structures, like the last node in a linked list.
• Error signaling in APIs.

Using null pointers helps in writing safe and defensive code, especially in memory-constrained embedded systems.

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