Does free(ptr) where ptr is NULL corrupt memory?
7.20.3.2 The
freefunctionSynopsis
#include <stdlib.h> void free(void *ptr);Description
The
freefunction causes the space pointed to byptrto be deallocated, that is, made available for further allocation. Ifptris a null pointer, no action occurs.
See ISO-IEC 9899.
That being said, when looking at different codebases in the wild, you'll notice people sometimes do:
if (ptr) free(ptr);This is because some C runtimes (I for sure remember it was the case on PalmOS) would crash when freeing a NULL pointer.
But nowadays, I believe it's safe to assume free(NULL) is a nop as per instructed by the standard.
All standards compliant versions of the C library treat free(NULL) as a no-op.
That said, at one time there were some versions of free that would crash on free(NULL) which is why you may see some defensive programming techniques recommend:
if (ptr != NULL) free(ptr);
If ptr is NULL, no operation is performed.
says the documentation.