No way to check, you ought to NULL initialize and then test whether NULL indeed
From section 7.20.3.2 The free function of C99 standard:
The free function causes the space pointed to by ptr to be deallocated, that is,
made available for further allocation. If ptr is
a null pointer, no action occurs. Otherwise, if the argument does not
match a pointer earlier returned by the calloc, malloc, or realloc
function, or if the space has been deallocated by a call to free or
realloc, the behavior is undefined.
