The C++11 standard generalizes the concept of constant expressions and introduces a new keyword constexpr as a declaration specifier. A constant expression is an expression that can be evaluated at compile time by the compiler. The major benefits of this feature are as follows:

• Improves type safety and portability of code that requires compile-time evaluation
• Improves support for systems programming, library building, and generic programming
• Improves the usability of Standard Library components. Library functions that can be evaluated at compile time can be used in contexts that require constant expressions.

An object declaration with the constexpr specifier declares that object to be constant. The constexpr specifier can be applied only to the following contexts:

• The definition of an object
• The declaration of a function or function template
• The declaration of a static data member of a literal type

If you declare a function that is not a constructor with a constexpr specifier, then that function is a constexpr function. Similarly, if you declare a constructor with a constexpr specifier, then that constructor is a constexpr constructor.

With this feature, constant expressions can include calls to template and non-template constexpr functions, constexpr objects of class literal types, and references bound to const objects that are initialized with constant expressions.

Evaluations of floating-point operations at compile time use the default semantics of the -qfloat option.