Stack vs Heap: Be Sure You Know Where Your Variables Live

https://www.youtube.com/watch?v=TP3_ZWncjqI Look at this function: int * make_int ( void ) { int x = 42 ; return & x ; // returning a pointer to a local } Now look at the caller: int * p = make_int (); foo (); // some other function printf ( "%d \n " , * p ); // ? It builds. The compiler may print a warning, but it builds. And then it lies — sometimes printing garbage, sometimes printing 42, sometimes crashing. Welcome to undefined behavior : the C standard makes no promises about what runs.