Why does -1 become -842150451 in C++?

Question

struct myclass {
    int id;
    myclass(): id(-1){};
};

myclass *a;
cout >> a->id;

This above is a demonstration of my long program. The output should be -1. But I do not know why the output becomes -842150451.

With `a->blubb` you are dereferencing an invalid pointer value which is undefined behaviour. — Swordfish, Oct 22 '18 at 18:39
@Swordfish Please, answer in the answer section or not at all. — Lightness Races in Orbit, Oct 23 '18 at 13:22

score 8 · Accepted Answer · answered Oct 22 '18 at 18:39

8

You have Undefined Behavior!

You create a myclass pointer, but never point it to anything. And then you try to dereference the dangling or wild pointer.

Try this instead to get the -1 you're expecting:

myclass a;
std::cout << a.id;

answered Oct 22 '18 at 18:39

scohe001

1 Answers1