static member variable's in-class assignment

Question

Here is the code,

class A { public: static A *get_a() { if(_pa == 0) _pa = new A; return _pa; } private: static A *_pa = 0; //cannot compile };

In the above code, if I move _pa's definition outof the class,

A * A::_pa = 0; //can compile

My problem is, static A *_pa = 0 inside the class body is just a declaration, not a definition, right?

Moreover, is it valid to assign a value to a static data member inside the class?

1) Correct, it doesn't even work in C++11, as all that does is sub it in where it would normally be default-initialized (i.e., when an object is created). 2) Yes, static variables can be accessed through the class itself, or objects. — Qaz
– Qaz, Commented Jul 25, 2012 at 6:32
possible duplicate of How to initialize a static member in C++? — RedX
– RedX, Commented Jul 25, 2012 at 7:32

MFH · Accepted Answer · 2012-07-25 06:33:34Z

Unless it's a const integral type (char, short, int, ...) you have to define the static member in a .cpp-File in addition to the declaration in the header.

header: class XYZ { static XYZ * instance; }; //cpp: XYZ * XYZ::instance;

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