🚀 go-pugleaf

I was wondering if someone could tell me exactly what behaviour is guaranteed 
for the mem library functions when n=0. I presume the answers are:

memcpy()  -> do nothing
memmove() -> do nothing
memset()  -> do nothing
memcmp()  -> return 0
memchr()  -> return NULL

But are these guaranteed?

Also, when n=0 is it guaranteed that these functions will not dereference 
their other arguments? 

Basically, I'm interested whether I can safely use something like:

memcpy(ptr,NULL,0);

or whether I have to wrap it:

if(len>0) {
    memcpy(dest,src,len);
}

Thanks,

Chris