CODEWITHSUNDEEP
crealloc
eladon19153
eladon19153

Reputation: 21

Does realloc deallocate before trying to allocate new memory?

I'm having trouble with my exercise here - I want to know about the realloc function a bit more -

If we send a pointer to the realloc, and it fails to allocate memory [returns null] does the memory that used to be allocated, now deallocated? although we failed?

ePointer = (Element*)realloc(stack->content, (sizeof(Element) * capacityOfStack(stack) * 2));

when stack->content being the pointer ofcourse, if we failed now have ePointer as NULL, then stack->content is no longer allocated?

Thanks alot!!

Upvotes: 0

Views: 337

Answers (4)

Arush Agarampur
Arush Agarampur

Reputation: 1430

realloc() does not de-allocate before trying to allocate again. What it does is first try to allocate a new block. If it fails, it returns and the old pointer is still valid. If it succeeds, then it copies the content from the original block into the new block, and then calls free() on the original block.

Upvotes: 0

ikegami
ikegami

Reputation: 386706

From man 3 realloc

If realloc() fails, the original block is left untouched; it is not freed or moved.

Upvotes: 1

Seva Alekseyev
Seva Alekseyev

Reputation: 61398

stack->content is still valid. If realloc fails, it returns NULL, but the old block of memory remains valid, that's the interface.

https://en.cppreference.com/w/c/memory/realloc

Upvotes: 2

user3657941
user3657941

Reputation:

From the man page for realloc:

    For realloc(), the input pointer is still valid if reallocation failed.

Upvotes: 3

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