Should I use constexpr or const?
When applied to functions the basic difference is this: const can only be used for non-static member functions, not functions in general. constexpr can be used with both member and non-member functions, as well as constructors. It declares the function fit for use in constant expressions.
What is constexpr keyword in C++?
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.
Is constexpr implicitly const?
Problem. In C++11, constexpr member functions are implicitly const. This problem only exists for the implicit this parameter to a function; constexpr functions can have parameters of (non-const) T * and T &.
Why do we use constexpr?
So, why do we need constexpr? The primary usage of constexpr is to declare intent. If an entity isn’t marked as constexpr – it was never intended to be used in a constant-expression; and even if it is, we rely on the compiler to diagnose such context (because it disregards our intent).
Does constexpr improve performance?
In Conclusion. constexpr is an effective tool for ensuring compile-time evaluation of function calls, objects and variables. Compile-time evaluation of expressions often leads to more efficient code and enables the compiler to store the result in the system’s ROM.
Is constexpr always static?
3 Answers. The short answer is that not only is static useful, it is pretty well always going to be desired. First, note that static and constexpr are completely independent of each other. static defines the object’s lifetime during execution; constexpr specifies that the object should be available during compilation.
Are constexpr functions inline?
While constexpr does imply inline for functions, it does not have that effect for non-static variables, considering C++17 inline variables.
Is constexpr variable inline?
Also, note that constexpr variables are inline implicitly, so there’s no need to use constexpr inline myVar = 10; .
What is a constant expression in C++?
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.
Is constexpr always evaluated at compile time?
The constexpr function is executed in a context which is evaluated at compile time. This can be a static_assert expression such as with the type-traits library or the initialisation of a C-array.
Does constexpr have to be static?
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.
What is difference between constexpr and Const?
The primary difference between const and constexpr variables is that the initialization of a const variable can be deferred until run time. A constexpr variable must be initialized at compile time. A variable can be declared with constexpr , when it has a literal type and is initialized.
When do you use a const variable instead of constexpr?
const can only be used with non-static member function whereas constexpr can be used with member and non-member functions, even with constructors but with condition that argument and return type must be of literal types. You read about more limitations here. Where to Use What?
When to use constexpr?
A constexpr integral value can be used wherever a const integer is required, such as in template arguments and array declarations. And when a value is computed at compile time instead of run time, it helps your program run faster and use less memory.
What is the difference between const and static readonly?
The difference is that the value of a static readonly field is set at run time, and can thus be modified by the containing class, whereas the value of a const field is set to a compile time constant. static readonly is typically used if the type of the field is not allowed in a const declaration, or when the value is not known at compile time.
What is the difference between constructor and destructor?
A constructor and destructor have the same name as the class, but the destructor has a tilde (~) sign. The key difference between a constructor and destructor is that a constructor is used to allocate memory to an object while a destructor is used to the deallocate memory of an object.