Discussion
What will be the output of the following C code?
#include <stdio.h>
int main()
{
int i = 10;
int *p = &i;
foo(&p);
printf("%d ", *p);
printf("%d ", *p);
}
void foo(int **const p)
{
int j = 11;
*p = &j;
printf("%d ", **p);
}
Answer: B
Correct answer: 11 11 Undefined-value
int **const p makes p itself const but leaves *p modifiable, so *p = &j is legal and main's pointer is redirected to j.
The first two prints show 11. But j is local to foo, and its lifetime ends when foo returns, so the pointer left in main is dangling. The second print in main reads that dead stack slot, which may still hold 11 or may not - it is undefined behaviour, and the intervening call to printf is exactly the sort of thing that overwrites it.
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