Question

Isn’t this supposed to produce a segfault?
When I run the code the output is 5. Example: http://ideone.com/gV2Nv

#include <iostream>
using std::cout;
using std::endl;

int* foo(int a) {
  int b = a;
  int* c = &b; 
  return c;
}

int main() {
  int* a = foo(5);
  cout << *a << endl; 
  return 0;
}

Answer 1

Returning an pointer to an local variable in the function is an Undefined Behavior.

Undefined Behavior does not warranty a segmentation fault. It merely means that any behavior is possible and the program can behave in any way.

It is a common misconception that Undefined Behavior means the code should produce a segmentation fault, the truth is that standard does not require any specific behavior in cases where the code invokes an Undefined Behavior and hence the name.

C++ Standard section 1.3.24 states:

Permissible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message), to terminating a translation or execution (with the issuance of a diagnostic message).