Initialization of static variables

You initialize a static object with a constant expression, or an expression that reduces to the address of a previously declared extern or static object, possibly modified by a constant expression. If you do not explicitly initialize a static (or external) variable, it will have a value of zero of the appropriate type, unless it is a pointer, in which case it will be initialized to NULL.

A static variable in a block is initialized only one time, prior to program execution, whereas an auto variable that has an initializer is initialized every time it comes into existence.

A static object of class type will use the default constructor if you do not initialize it. Automatic and register variables that are not initialized will have undefined values.