Local variable on the stack not getting deleted when out of scope

Question

#include <iostream>

int* retPointer()
{
    int x=10; //same as auto int x =10;
    return &x;
}

int main(int argc, char **argv)
{
    std::cout<<"x="<<*retPointer()<<std::endl;
    return 0;
}

In the example above I am returning a pointer that points to a local variable to stack. When I print the value pointed by this pointer in the man() then I should get a seg-fault. The variable x should go out of scope when I return from function retPointer(). So when try to access the value in main() should I not get a segmentation fault? Am I missing something here?

Output is = x=10

Are you sure this works? Well, the stackframe is lost, but the memory still exists after the function terminates, but actually it shouldn't happen... — bash.d, Feb 20 '13 at 15:47
look at [this code](http://liveworkspace.org/code/2LgTCL$2) to ensure, that you're wrong — borisbn, Feb 20 '13 at 15:53
borisbn- I have copied and pasted your code. I still get Hi x=10. I understood that its a undefined behavior. I am using MinGW 64 bit compiler in windows. — Soumyajit Roy, Feb 20 '13 at 17:10

Andy Prowl · Answer 1 · 2013-02-20T15:52:30.260

The x object does go out of scope when returning from retPointer(), and dereferencing a pointer to an object whose lifetime has expired is Undefined Behavior.

A program having Undefined Behavior means that anything could happen, including a crash, behaving as if nothing happened (like *retPointer() returning a normal value such as 10), or formatting your hard drive.

Although the last option is quite unlikely, you definitely do not want to have Undefined Behavior in your program. Do not ever return pointers or references to local objects with automatic storage.

score 0 · Answer 2 · answered Feb 20 '13 at 15:46

0

When I print the value pointed by this pointer in the man() then I should get a seg-fault.

You should? Where in the spec does it say this will happen?

You're invoking undefined behaviour. Anything could happen.

answered Feb 20 '13 at 15:46

James M

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Local variable on the stack not getting deleted when out of scope

2 Answers2