C++ code question ( 8 )

Question

What is the output of this code?
int a[5] ={1,2,3,4};
int *p = a;
cout<<*(p + 4);
This question maybe is too simple for you, but it's a stumbling block for me , could you give me a hand 🙁?

Answer 1

well there you go, :) one would have assumed uninitialised array values would produce garbage in the same way uninitialised variables do :)

but, no. clearly they are auto assigned 0

The more you know :)

Answer 2

Arrays are contiguous chunks of memory filled with homogeneous types ( in your sample with 32Bit integer types ).

int a[5]
____
|__1_| <- a[0], address -> 0x0021FCC4
|__2_| <- a[1], address -> 0x0021FCC8
|__3_| <- a[2], address -> 0x0021FCCC
|__4_] <- a[3], address -> 0x0021FCD0
>>>>>>> last element is filled with zero by default.
|__0_] <- a[4], address -> 0x0021FCD4

int *p = a or 0x0021FCC4;

print -> content of the address of the last element which pointed by p (if *p dereference 1, then *(p+1) dereference 2, *(p+2) dereference 3 all the way down to the last element)

Answer 3

you have declared array of 5 element but you only assigned value to the first 4 elements

so....by default compiler initialize 5th element with 0.

but if you will try to print values outside the array range like*(p+5) or anything then it would print garbage values.

Answer 4

int most languages if some array values are not defined they automatically set to default value of that type of array(array values), so in this case output is 0

Answer 5

Hey people, don't confuse undefined behaviors whit yours gaps!
Please do some checks before talking about it.
You won't learn anything if you do so.

Very good @JPM7 you know your stuffs!

I was just reading it, in sum if you want to initialize an array at zero you could do like this:
int arr [n]={};

Answer 6

@alice .. Tanay is wrong too.. only JPM7 is correct.

Answer 7

Thank you Babak Sir, and nice to see you again dearest bro!

Answer 8

Late to the Discussion, not here for adding anything, instead, learn from everyone here, just wanted to thank @All, I learned something new (again) from this discussion. kinda wish we could have loads more of such discussions like this, something worth reading and knowing. I'm definitely bookmarking this thread.

Thanks @Everyone : )

Answer 9

thank you for knowing what you are talkin about lol
Whit respect for people that didnt, I understand.. we all want to help but sometimes we do damages.

Answer 10

Thanks to all who answered this question

Answer 11

message received , thanks for your time.

Answer 12

The output is 0@Timon Paßlick

Answer 13

why is it zero? @ Timon Paßlick

Answer 14

I'm still confused .

Answer 15

Thanks @Shah Tanay , I got it 😄

Answer 16

Thank you , I know the answer but I don't know how to get it

Answer 17

@JPM7 When I say that something is wrong and misleading, I use to give very good reasons.
Is it because I said that it is out of the array although technically speaking, it's inside the array but uninitialized?
Come on, she's a beginner! She wanted a simple explanation, nothing is entirely true.

Answer 18

Ok, got it. The comments were enough. Are these rules also valid for stl containers and initializer_lists?

Answer 19

They do, but it's just 0 in many cases because memory looks like this (power off) before you assign the first variable to it. It's undefined because for example deleted values don't get set to 0.

Answer 20

I knew all of that except that it depends on the containers constructor.