Can static member variables be initialized via member initialization list?

Question

I tried to initialize a static member variable with a member initialization list. But I got errors like

static variable cannot be initialized via constructor

For example, my class sample has a static member variable y of type int. I couldn't do this:

sample(int a):y(a){}

Why is that so?

Maybe read a book to learn the basics? https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list — Galik, Jun 30 '16 at 21:50
@Deepika If you made a mistake in your question, you can [edit] it to fix it. — Baum mit Augen, Jun 30 '16 at 22:00

Baum mit Augen · Accepted Answer · 2016-07-04T15:59:34.893

A static member variable does not belong to a single instance of your class. So when a constructor (which is a function that initializes an instance) runs, the static member already is initialized. You cannot initialize it again.

You can however assign to it in the constructor's body:

sample(int a) {y = a;}

though that will rarely be useful.

Again, remember: Every time a constructor runs, it constructs one instance, while static members exist across all instances.

score 0 · Answer 2 · edited Jul 04 '16 at 17:10

A static member is per-class, not per-instance, so a static member will only be constructed once in the lifetime of the program. A constructor is invoked every time you make an instance of the class.

What you want to do is initialize the static member inside of a .cc file that will be liked in.

Something like :

// Foo.h

class Bar {
    public :
       Bar(int) {
       }

};

class Foo {
  public:
         static Bar MrStatic;
};

// Foo.cc

Bar Foo::MrStatic(10);

Can static member variables be initialized via member initialization list?

2 Answers2