What is the correct usage of realloc() when it fails and returns NULL?

Question

Can anyone summarize what is the correct usage of realloc()?

What do you do when realloc() fails?

From what I have seen so far, it

Answer 1

If realloc fails I don't think you would want to delete the original block since you will lose it. It seems like realloc will resize the old block (or return a pointer to a new location) and on success will return a pointer to the old block (or new location) and on failure will return NULL. If it couldn't allocate a new block the old block is untouched.