Why does gcc printf(%s, array) correctly output a char array that is not a NULL-terminated string?

Question

C++ / C#

#include <stdio.h>

int main() {
    char foo[6] = {"123456"};
    printf("%s", foo); // 123456
}

Why is gcc outputting the given array correctly? After all, the specifier %s means to display all the characters in the array until it encounters \0. But it is clearly not set. I expected to see just a stream of random bytes from memory until I encountered \0 somewhere.

Answer 1

Lucky. The next address after the array contains zero. The array is created on the stack. Your simple program doesn't litter the stack. It is likely that the next element is simply 0. Look in the debugger for the value of foo[6] or print