constexpr specifies that the value of an object or a function can be evaluated at compile time and the expression can be used in other constant expressions. For example, in below code product() is evaluated at compile time. In C++ 11, a constexpr function should contain only one return statement..
Beside this, what is Constexpr used for?
The constexpr specifier declares that it is possible to evaluate the value of the function or variable at compile time. Such variables and functions can then be used where only compile time constant expressions are allowed. A constexpr specifier used in an object declaration implies const.
Furthermore, is Constexpr evaluated? 2 Answers. constexpr functions will be evaluated at compile time when all its arguments are constant expressions and the result is used in a constant expression as well.
Moreover, when should I use Constexpr?
constexpr indicates that the value, or return value, is constant and, where possible, is computed at compile time. A constexpr integral value can be used wherever a const integer is required, such as in template arguments and array declarations.
Are Constexpr functions inline?
You can perform with constexpr functions a lot of calculations at compile time. Therefore, the result of the calculation is at runtime as a constant in ROM available. In addition, constexpr functions are implicit inline. The syntax of constexpr functions was massively improved with the change from C++11 to C++14.
Related Question Answers
What is a literal type?
A literal type is a type that can qualify as constexpr. This is true for scalar types, references, certain classes, and arrays of any such types. A class that is a literal type is a class (defined with class, struct or union) that: has all non-static data members and base classes of literal types.What is static Constexpr?
static constexpr int a = 2; constexpr int a = 2; Static specifies the lifetime of the variable. A static constexpr variable has to be set at compilation, because its lifetime is the the whole program. Without the static keyword, the compiler isn't bound to set the value at compilation, and could decide to set it later.Is Constexpr static?
static defines the object's lifetime during execution; constexpr specifies that the object should be available during compilation. Compilation and execution are disjoint and discontiguous, both in time and space. So once the program is compiled, constexpr is no longer relevant.What is inline in C++?
C++ inline function is powerful concept that is commonly used with classes. If a function is inline, the compiler places a copy of the code of that function at each point where the function is called at compile time. The compiler can ignore the inline qualifier in case defined function is more than a line.What is a constant expression in C++?
A constant value is one that doesn't change. C++ provides two keywords to enable you to express the intent that an object is not intended to be modified, and to enforce that intent. C++ requires constant expressions — expressions that evaluate to a constant — for declarations of: Array bounds.What is an inline function in C++?
C++ provides an inline functions to reduce the function call overhead. Inline function is a function that is expanded in line when it is called. This substitution is performed by the C++ compiler at compile time. Inline function may increase efficiency if it is small.What is an inline variable?
Inline variables. A variable declared inline has the same semantics as a function declared inline: it can be defined, identically, in multiple translation units, must be defined in every translation unit in which it is used, and the behavior of the program is as if there was exactly one variable. 
