C++ In a Nutshell

Constant Expressions

A constant expression is an expression that can be evaluated at compile time. Constants of integral or enumerated type are required in several different situations, such as array bounds, enumerator values, and case labels. Null pointer constants are a special case of integral constants.

Integral Constant Expressions

An integral constant expression is an expression that can be evaluated at compile time, and whose type is integral or an enumeration. The situations that require integral constant expressions include array bounds, enumerator values, case labels, bit-field sizes, static member initializers, and value template arguments. The compiler must be able to evaluate the expression at compile time, so you can use only literals, enumerators, const objects that have constant initializers, integral or enumerated template parameters, sizeof expressions, and constant addresses. The address of a static lvalue object is a constant address, as is the address of a function. A string literal, being a static array of characters, is also a constant address.

An integral static const data member can be initialized in the class definition if the initializer is a constant integral or enumerated expression. The member can then be used as a constant expression elsewhere in the class definition. For example:

template<typename T, size_t size>
class array {
public:
  static const size_t SIZE = size;
  ...
private:
  T data[SIZE];
};

See Chapter 6 for more information about static data members. ...