What Every C Programmer Should Know About Undefined Behavior (2011)

Re:What Every C Programmer Should Know About Undefined Behav... by 0xcde4c3db on Thursday January 05, 2017 @09:51AM (#13327479)

> if P does not point to valid memory, then dereferencing it is UB

IIRC, simply making P point to anything other than an object or 1 past the end of an array is already UB. I suspect that this is because some architectures have dedicated address registers and can take an exception when an invalid address is loaded/calculated instead of doing it when the memory access happens.

[ Parent | on HN ]

Re:What Every C Programmer Should Know About Undefined Behav... by lmm on Thursday January 05, 2017 @09:58AM (#13327535)

> IIRC, simply making P point to anything other than an object or 1 past the end of an array is already UB.

I don't think this is true in the strict sense you're describing it. Certainly forming a null pointer isn't UB as I understand it, only dereferencing one.

[ Parent | on HN ]

Re:What Every C Programmer Should Know About Undefined Behav... by 0xcde4c3db on Thursday January 05, 2017 @10:28AM (#13327831)

Yes, NULL is another exception that I forgot. I'm not sure this is ever explicitly stated as a distinct rule in the standard, but it seems to be implied by various arithmetic and conversion operations on pointers being UB if the result doesn't point to a valid object.

[ Parent | on HN ]