CODEWITHSUNDEEP
cstack
user1978273
user1978273

Reputation: 514

Predict the output of the C code

I attended an interview where this code was written and I had to predict the output of the code.

int foo() {
  int a;
  a = 5;
  return a;
}

void main() {
  int b;
  b = foo();
  printf ("The returned value is %d\n", b);
}

The answer was so obvious to me and I answered 5. But the interviewer said the answer is unpredictable since the function would have been popped from the stack after return. Could anyone kindly clarify me on this?

Upvotes: 0

Views: 522

Answers (1)

John Hascall
John Hascall

Reputation: 9416

The code as you have presented it does not have the problem the interviewer asserted it does. This code would:

#include <stdio.h>

int * foo ( void ) {
    int a = 5;               /* as a local, a is allocated on "the stack" */
    return &a;               /* and will not be "alive" after foo exits */
}                            /* so this is "undefined behavior" */

int main ( void ) {
    int b = *foo();          /* chances are "it will work", or seem to */
    printf("b = %d\n", b);   /* as we don't do anything which is likely */
    return 0;                /* to disturb the stack where it lies in repose */
}                            /* but as "UB" anything can happen */

Upvotes: 6

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