Warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11? [duplicate]

Answer 1

You asked:

Edit: And what is the difference between a static member initializer and non-static member initializer?

Not much different.
The intializer to initialize a static member is a static member initializer.
The intializer to initialize a non-static member is a non-static member initializer.

class foo
{    
    static int var2 = 20;  // static member initializer
    int var1 = 10;         // non-static member initializer
};