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

Edit: Correction, some people are bashing me for what I said, the way you allocated your pointer seems to be best practice among them, I was taught to always go with type casts in the sizeof(), but apparently your way is more correct, so disregard what I said =)

Taking a peek at http://en.wikipedia.org/wiki/Malloc#realloc before might have done you some good.

You don't quite understand sizeof() - it has the value of the size of the argument you pass to it in bytes. For example, sizeof(int) will be 4 on most 32 bit systems but you should still use sizeof(int) instead of 4 because compiling your code on a 64 bit system (just as an example) will make that value equal to 8 and your code will still compile fine. What are you allocating memory for? Pointers? If so you should use sizeof(void*) instead (you can say sizeof(int*) but it's common convention not to mention to the compiler what you want to store at those pointers, since all pointers should be the same size - so most programmers say sizeof(void*)), if you need space for characters use sizeof(char) and so on.

You are however right to store the return value of realloc() in a new pointer and check it, though a lot of programmers will assume the system always has enough memory and get away with it.