returning reference to local variable in C++

Question

is the below code wrong ? I am returning reference to local variable ...it should core dump , but it is executing fine . Is the below code is working fine on my system because I am LUCKY ??

#include<iostream>
using namespace std;

class a{
    public:
    int i;
    int arr[20];
    a()
    {
        cout<<"\ninside constructor";
        i=10;
    }
    public:
    static a& ret()
    {
        a chk;
        return chk;
    }
    void say()
    {
        i=10;
        arr[0]=1;
        cout<<"\nHello World\n";
    }

};


int main()
{
(a::ret()).say();
return 1;
}

It *shouldn't* do anything. Undefined behavior as it's name implies is... well... undefined. Anything can happen, it's a surprise! — Borgleader, Jul 04 '13 at 18:01
["Somebody told me that in basketball you can't hold the ball and run. I got a basketball and tried it and it worked just fine. He obviously didn't understand basketball."](http://c-faq.com/ansi/experiment.html) — Jonathan Wakely, Jul 04 '13 at 18:24

score 8 · Answer 1 · answered Jul 04 '13 at 18:00

8

it should core dump - nope. It's undefined behavior, anything can happen, including appear to work (which sucks, because it can hide bugs).

Is the below code is working fine on my system because i am LUCKY ??

No, because you're unlucky.

answered Jul 04 '13 at 18:00

Luchian Grigore

253,575
64
457
625

yeah ..it should be unlucky for me... – user1057741 Jul 04 '13 at 18:03
@user1057741 its best case, worst case would be if your this code run fine – Grijesh Chauhan Jul 04 '13 at 18:05

score 5 · Answer 2 · answered Jul 04 '13 at 18:00

5

i am returning reference to local variable ...it should core dump

Wrong. it is undefined. it can do whatever it likes to. The object was on the stack, it is still accessible, so you can work with it.

Yes, you are lucky. If it was in real code, it wouldn't be considered as a good luck; "This code contains a serious bug, but it happens to be working fine. Am I lucky"? answer it yourself.

answered Jul 04 '13 at 18:00

Elazar

20,415
4
46
67

int *p=new int[10]; delete p; delete p; is double delete is undefined or will surely core dump ?? – user1057741 Jul 04 '13 at 18:04
Undefined. But I think in reality will probably crash. – Elazar Jul 04 '13 at 18:06
1

@user1057741: The standard says nothing about core dumps or crashes. Undefined and core dump are not mutually exclusive. – Benjamin Lindley Jul 04 '13 at 18:16
@user1057741 try in this code to make another call to some function, and the access the object returned earlier. It will probably not work fine. – Elazar Jul 04 '13 at 18:28

returning reference to local variable in C++

2 Answers2