What happens to uninitialized class members in c++?

Question

What happens to uninitialized class members in c++? If I have to do this, what should I take care of?

#include <iostream> 
using namespace std;

class Foo {
    int attr1, attr2;   
public:
    Foo ();

Foo::Foo () {   attr1 = 5; }

Foo myThing();

attr2 will contain garbage value – Asesh Sep 01 '17 at 15:15 — Asesh, Sep 01 '17 at 15:15

score 4 · Accepted Answer · answered Sep 01 '17 at 15:17

4

What happens to uninitialized class members in c++?

They are default initialized, which in case of fundamental types like int means that it will have an indeterminate value.

what should I take care of?

You should take care to never read an indeterminate value.

answered Sep 01 '17 at 15:17

eerorika

1

@Taylor You should start a habit of initializing variables when you declare them or in the constructors. – Thomas Matthews Sep 01 '17 at 15:48
@ThomasMatthews i already have this habit – Taylor Sep 03 '17 at 16:59
@Taylor: You need more diligence. The variable `attr2` is not initialized in your constructor. – Thomas Matthews Sep 03 '17 at 17:59

score 2 · Answer 2 · answered Sep 01 '17 at 15:17

2

They are default-constructed.

For nested classes this means these have to have a constructor that can be called without arguments.

For plain old data members (int et. al.) this means they simply stay uninitialized as any other local variable would.

answered Sep 01 '17 at 15:17

Kamajii

2 Answers2