“C is how the computer works” is a dangerous mindset for C programmers

Post by pcwalton » Tue, Mar 31, 2020, 6:10 PM UTC

infamouscow wrote: post #38

antirez wrote: post #6

Actually I look forward for enough momentum to be created in the community, to allow new C standards to change the way undefined behaviors are conceived, and make them as specified as possible, and even when they cannot in reasonable unique ways, to provide reference possible behaviors to select in order to have the least unexpected outcome for the programmer. Especially now that low level programming is abstracting…

It would also be nice if Rust had a specification. Without a spec it's impossible to build a correct alternative Rust implementation.

Post by saagarjha » Tue, Mar 31, 2020, 6:15 PM UTC

throwaway_pdp09 wrote: post #191

eternalban wrote: post #168

Earlier quoted context omitted.

No. It is not "undefined behavior". The "behavior" here is assignment (reading memory). It always will behave precisely and consistently: it _will_ assign the "indeterminite" value of the un-initialized memory. Using such an "indeterminite value" in other operations (e.g comparison per the link Steve B. posted above: https://www.ralfj.de/blog/2019/07/14/uninit.html ) is the UB bit.

> [reading memory} always will behave precisely and consistently What is the point of not making it UB? You can't AFAICS possibly rely on any useful way on it behaving 'precisely and consistently' so just make it UB anyway?

Post by saagarjha » Tue, Mar 31, 2020, 6:16 PM UTC

chrisseaton wrote: post #84

radarsat1 wrote: post #81

Earlier quoted context omitted.

> pointer provenance, inability to read uninitialized memory what do you mean by these two? not sure about the former. as for the latter, of course you can read uninitialized memory, unless you mean something else?

Can you write a well-defined C program that reads uninitialised memory?

Post by saagarjha » Tue, Mar 31, 2020, 6:20 PM UTC

amiga_500 wrote: post #244

saagarjha wrote: post #228

Earlier quoted context omitted.

What are you comparing it to? I think C++ tooling is fairly decent. (By the way, what do you work on?)

I think java has very good tooling. Java's main issue is the barrier to entry is lower because it has good tooling, which means really bad, inexperienced programmers can write bad code, and have more tooling to bail them out, allowing them to continue down that path until they have a huge ball of mud. There ought to be some kind of phrase for this "the tooling curse". GDB isn't bad, IMHO, but the inability of IDEs to…

Post by icedchai » Tue, Mar 31, 2020, 6:23 PM UTC

hexane360 wrote: post #136

gruez wrote: post #91

Earlier quoted context omitted.

>inability to read uninitialized memory printf("%x", *(int*)0x12345678);

Even casting 0x12345678 to int* is undefined behavior