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I've used the free function to free an array that was part of a struct. However I got some segfaults when running the program, so I decided to print out the array to see what had happened to it.
I saw that the buffer had a mix of garbage values and part of the original string.
Essentially, I had called free like:
then I didCode:free(node->string);
got garbage as a result. Isn't free() supposed to null whatever you are meant to be freeing?Code:printf("%s", node->string);
NoQuote:
Isn't free() supposed to null whatever you are meant to be freeing?
it just markes a reageon as availeble for usage, it does not modifies memory contents, and does not updates your pointer with null value,
using the freed pointer - is undefined behavior
That's because it's undefined behaviour. It can crash. It can not crash. It is not guaranteed to crash either.
The rule is: just don't do it.
Free simply tells the operating system you don't want that piece of memory any more. Then it's up to the OS what it wants to do with it.
Hmm, I seemed to have stopped the segfaults, a stray something somewhere.
But if I free the memory in array in a struct, then I can malloc that memory again right? Without having to create a new node all the time.
Sure you can. The memory is now free and unusable, so you need to malloc again to use a new piece.
Cheers
if you create a temporary variable so that you store a copy of the node in that variable.
And you then free the node, why does the temporary variable also get freed?
No, not if you make a copy. Since pointers do just contain addresses, if you have two pointers to the same data and if you free one, the other will also be freed.
But if you make a copy, then they will have two different addresses and thus only one gets freed.
Ahhhhhh pointers, that's what I did by mistake, I created a pointer instead of making a node and then assigning it. No wonder it got freed too.
Thanks Elysia. You're a programming master! How the hell do you know every thing? ;)