ios_base and static members

Static constants in the ios_base class are initialized when created, which makes sense for constants. Can non-constant static member variables be initialized the same way, or is this concept only allowed for constant static members?

For non-constant static members with gnu compilers must use always开发者_开发百科 define/allocate space separately from it's deceleration in the header? Is it even proper to initialize constant static members this way?

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Class members can be created and initialized only for the static const (integral data type, like int, char, double etc.) members in current C++ standard. For non-static member it's not possible. However, in C++0x that facility is introduced.

Edit: For non-const static member, you can do initialization but you have to do the same in .cpp file (for non template classes). e.g.

struct A
{
  static const int i = 0; // ok
  static int j;  // can declare in .cpp file as below
  int k = 2; // error, but valid in C++0x
  const int l = 3; // error, valid in C++0x
  static const int m[2] = {1,2}; // error, should be an integral type
  static const string n = "hi"; // error, should be an integral type
};
int A::j = 1  // declare in class body, and define outside

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Because static data members must be explicitly defined in exactly one compilation unit.

From C++ FAQ http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.12

You might want to read the whole "Constructors" section about "static data member" to clearly understand it. http://www.parashift.com/c++-faq-lite/ctors.html