What happens when the call free (ptr); is executed and ptr is NULL? If you do not know, read about the behavior of the free() function. I like this reference: https://www.cplusplus.com/reference/cstdlib/free/c The code does not compile. The code compiles and runs, but gives segmentation fault. The code runs, but the behavior will be undetermined. The library page on this (from the included link) does not say and so I do not know. The code runs and the function does nothing