Memory Allocation · Memory Allocation MCQ · Question 3

What does free(NULL) do in C? Answer, explanation & discussion

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Question 3 Back to Exercise

What happens when you call free(NULL)?

A The program crashes
B Nothing – it is defined to do nothing Correct
C It frees the last allocated block
D It is undefined behaviour

Correct Answer: Option B

The standard says free(NULL) has no effect. That is why setting a pointer to NULL after freeing it makes an accidental second free() harmless, and why cleanup code can free pointers that were never allocated.

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What does free(NULL) do in C? Answer, explanation & discussion

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