5 ms·

By the way, dereferencing NULL is a well defined behaviour on every computer architecture: you are basically reading at address 0 of memory. It just causes a cr

By the way, dereferencing NULL is a well defined behaviour on every computer architecture: you are basically reading at address 0 of memory. It just causes a crash if you have an operating system since it will cause a page fault, but in kernel mode or in devices without an OS is a legit thing to do (and even useful in some cases). Why should C compilers make it undefined? The standard doesn't mandate that undefined behaviour should change the semantic of the program. Just define all the undefined behaviour that you could, to me keeping them undefined makes no sense (even from the standard point, everyone knows that if you overflow an int it wraps around, why should it be undefined??)

foldr 5y ago
I’m not totally sure, but I think dereferencing a zero pointer is theoretically not undefined behavior in C, just so long as you didn’t obtain the zero pointer by initializing a pointer with a null pointer constant.
saagarjha 5y ago
NULL is not required to have a bit representation of all zeroes. If you are programming for a low-level hardware device, it might be worth your while to get a C implementation that does not represent the NULL pointer this way.
- Too 5y ago
  Pointers are hardly even required to have a bit representation at all! [1] This is one of the most common impedance mismatches between programmers and the C spec. C does not mention how the machine should handle memory. Variables and pointers are just abstract constructs there. While many programmers think their programs are a giant char* on their DRAM stick that can be fiddled with at any time and in any way they please. ([1] Actually this is not entirely true but it is better to think of them this way for the sake of not making more assumptions on the memory which are UB. Pointers are allowed to be converted to integer types - but with the caveat that alot of behaviour around it is implementation defined and of course surrounded with a big dose of UB as well!)
deleted 5y ago
[deleted]

foldr 5y ago

I’m not totally sure, but I think dereferencing a zero pointer is theoretically not undefined behavior in C, just so long as you didn’t obtain the zero pointer by initializing a pointer with a null pointer constant.

saagarjha 5y ago

NULL is not required to have a bit representation of all zeroes. If you are programming for a low-level hardware device, it might be worth your while to get a C implementation that does not represent the NULL pointer this way.

Too 5y ago
Pointers are hardly even required to have a bit representation at all! [1] This is one of the most common impedance mismatches between programmers and the C spec. C does not mention how the machine should handle memory. Variables and pointers are just abstract constructs there. While many programmers think their programs are a giant char* on their DRAM stick that can be fiddled with at any time and in any way they please. ([1] Actually this is not entirely true but it is better to think of them this way for the sake of not making more assumptions on the memory which are UB. Pointers are allowed to be converted to integer types - but with the caveat that alot of behaviour around it is implementation defined and of course surrounded with a big dose of UB as well!)

deleted 5y ago

[deleted]