Technically the allocation succeeded. That's why you have a pointer and not NULL. So the answer is the classic one: "you check if the pointer is NULL or not".

Technically the allocation succeeded. That's why you have a pointer and not NULL. So the answer is the classic one: "you check if the pointer is NULL or not". This entire thing is a wrong question to be asking, anyway. Even if you are sure right after malloc that "you have the memory 100% available to you", who's not to say that, immediately one nanosecond afterwards, some other process comes in and, well, asks for more memory? The memory you were so sure you had for yourself right after malloc may no longer be there (either swapped out or even discarded if possible), and you will be killed for trying to access it again. Oops. At no point you can say "I have this memory and it's mine and just mine!" unless you are root and mlock (or equivalents). And I hope you don't do that, anyway. Just let the OS do what it is designed to do.