Question

Does the following code invoke undefined behaviour? As far as I know we should always use new to create user defined objects dynamically because new in addition to malloc calls the constructor too.

#include <cstdio>
#include <cstdlib>

struct om
{
    int a;
    void fun()
    {
        a=10;b=10;
    }
    private : int b;

} s1; // structure(om) variable... 


typedef struct om node;

int main()
{
node *s2=(node *)malloc(sizeof(node));
s1.fun();
printf("%d",s2->a);
return 0;
}

The above code prints 0. That means s2->a is automatically initialized to 0?
So I want to know is the behaviour of the program Implmentation defined, Undefined or Well defined?

Answer 1

malloc isn’t guaranteed to initialize the memory it allocates – if you want the memory to be filled with 0’s then use calloc.