Deleting a pointer to an automatic variable [duplicate]

Question

This question already has an answer here:

• What is the behavior of “delete” with stack objects? [duplicate] 1 answer

Please look at this code

int i = 10;                                     //line 1 
int *p = &i;                                    //line 2  
delete p;                                       //line 3 
cout << "*p = " << *p << ", i = " << i << endl; //line 4  
i = 20;                                         //line 5  
cout << "*p = " << *p << ", i = " << i << endl; //line 6  
*p = 30;                                        //line 7
cout << "*p = " << *p << ", i = " << i << endl; //line 8  

What is the result of this code? Especially of line 3, 5 and 7? Do they invoke undefined behavior? What would be the output?

EDIT : I tried running it using g++, and it's compiling and running fine! I'm using MinGW on Windows 7.

What does Standard say in this context?

Answer 1

You can delete only a pointer if you have ever allocated it dynamically using new. In this case you have not allocated the pointer using new but simply defined and initialized it to point to a local variable of type int.

Invoking delete on a pointer not allocated dynamically using new is something called Undefined Behavior. In short, it means that anything on the earth can happen when such a code is executed and you can't complaint a bit to anyone on this planet.

Answer 2

delete p; is UB and so any further behavior can't be predicted or relied upon. You program might crash immediately or spend all your money or just exit from main() and pretend nothing happened.

Answer 3

Line 3 is definitely undefined behaviour, since you're trying to deleting memory at an address that is not on the heap.