What is the purpose of constexpr?
What is the purpose of 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.
Does C have constexpr?
No, no such thing exists in C.
How do I know if a function is constexpr?
The easiest way to check whether a function (e.g., foo ) is constexpr is to assign its return value to a constexpr as below: constexpr auto i = foo(); if the returned value is not constexpr compilation will fail.
When to use #define vs constexpr?
#define (also called a ‘macro’) is simply a text substitution that happens during preprocessor phase, before the actual compiler. And it is obviously not typed. constexpr on the other hand, happens during actual parsing. And it is indeed typed.
What is the difference between const and constexpr?
The principal difference between const and constexpr is the time when their initialization values are known (evaluated). While the values of const variables can be evaluated at both compile time and runtime, constexpr are always evaluated at compile time.
Is constexpr guaranteed?
A constexpr function that is eligible to be evaluated at compile-time will only be evaluated at compile-time if the return value is used where a constant expression is required. Otherwise, compile-time evaluation is not guaranteed.
Can you change a constexpr?
A const int var can be dynamically set to a value at runtime and once it is set to that value, it can no longer be changed. A constexpr int var cannot be dynamically set at runtime, but rather, at compile time. And once it is set to that value, it can no longer be changed.
Why is constexpr over const?
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.
Should I use const with 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.
Does constexpr need 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. So, what does constexpr mean?
Is C++14 extended constexpr supported in 2015 RTM?
As I previously mentioned, the compiler currently supports C++11’s original rules for constexpr. C++14 extended constexpr will be implemented in the future, but not in 2015 RTM. In the STL, we’ve implemented every occurrence of constexpr in the current C++17 Working Paper N4527, with a very small number of exceptions:
Is it possible to implement every occurrence of constexpr in STL?
In the STL, we’ve implemented every occurrence of constexpr in the current C++17 Working Paper N4527, with a very small number of exceptions: And by “implemented”, I mean that I’ve got a test case that exercises every occurrence of constexpr in the STL, which the compiler accepts without any workarounds.
What does vs 2015 update 1 mean for C++11 constexpr?
Our goal with VS 2015 Update 1 was to finish up the last significant feature work for C++11 constexpr and improve our implementation’s robustness. This blog post is going to provide some notes to explain where VS 2015 Update 1 puts us and where we’re going with constexpr support.
Does Visual Studio 2015 RTM support constant expressions?
Visual Studio 2015 RTM shipped with support for constant expressions as specified in the C++11 language standard. The release received lots of excellent feedback from our users and the C++ community. Using that feedback, we’ve been working on refining our implementation for VS 2015 Update 1.