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cmemoryfree
Mohamad-Jaafar NEHME
Mohamad-Jaafar NEHME

Reputation: 1215

Check if memory was already freed in C

As you know, after we finish using dynamic variables we free() them.

However, sometimes those variables are already free()d.

I need to check if it is free to avoid double free. Would anyone give me a clue?

Upvotes: 1

Views: 2458

Answers (2)

Ed Swangren
Ed Swangren

Reputation: 124692

You can't check if it's already been free'd (the signature of free should tell you that much; it can't modify the pointer from the caller's perspective). However, you can do one of two things.

  1. Change your design. Who is responsible for this memory? It seems as though your design does not make that clear, which is the most common reason for memory leaks. Place ownership on one part of your code and be done with it. Why would the interrupt function conditionally deallocate the memory? Why does that seem like the most logical solution?

  2. Set the pointer to null and double free all you like. free(NULL) is perfectly valid.

I prefer option 1 and learning this lesson now will help you write better code down the road.

Upvotes: 13

abligh
abligh

Reputation: 25129

+1 to Ed S.'s answer.

But also, run valgrind - it will pick up many dynamic memory allocation errors quickly, and may be better at reading your code than you are.

Upvotes: 4

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