i -= --i

Ranter

Deeshti

716

Comments

7

Mvzes

346

5y

i -= --i evaluates to i = 1 strangely enough. i'd imagine it evaluate to 0.
0

12bitfloat

9264

5y

@Mvzes The wonders of cache bleeding
4

asgs

11563

5y

@Mvzes strange? It is equivalent i - ( i - 1)
2

12bitfloat

9264

5y

@asgs The decrement is evaluated first. So i is decremented and then the value is subtracted from i (which again, should already be decremented). Thus it should be 0
2

Electrux

4299

5y

@Mvzes it evaluates to zero in C using the clang compiler 🤔
4

kraator

413

5y

@Mvzes That's why this code has undefined behavior in C. A variable cannot get updated more than once within a sequence point. Different compilers may generate different code for this.
3

asgs

11563

5y

@12bitfloat I was merely explaining why it was 1 in this case. It is clearly a UB.

Such kind of code can and must only appear in pointless puzzles
0

Pickman

656

5y

@Deeshti and that's why you do not use increment and decrement operators...
0

Tarak311

17

5y

it seems to increment the number, anyway I don't fucking care !!!!. Why anyone would do that... I yet to get job but anyone use this in real world? Why they ask this kind of questions in interview?
6

12bitfloat

9264

5y

@Tarak311 Maybe the reason you don't care has something to do with you not having a job
3

kraator

413

5y

@Tarak311 two possible reasons why they ask this in an interview :
A) they want you to say this code has UB.
B) they are idiots. If they don't know about UB you should look for a different employer 😉.
0

Pickman

656

5y

@kraator UB?

... Oh. Undefined behaviour.

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