Menu
With the new C++11 standard, when should I use the inline keyword over the constexpr keyword? Does the constexpr keyword offer any additional optimization over inline, or does it merely assert that things must be computed at compile-time?
Why does constexpr work on the GCC in some cases where the call is not constant, such as calling foo(x) on a non-constexpr variable? Is this a bug in the GCC or is it actually part of the standard?
546
A constexpr specifier used in a function or static data member (since C++17) declaration implies inline .
Understanding constexpr Specifier in C++ constexpr is a feature added in C++ 11. The main idea is a performance improvement of programs by doing computations at compile time rather than run time. Note that once a program is compiled and finalized by the developer, it is run multiple times by users.
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.
Yes. I believe putting such const ness is always a good practice wherever you can. For example in your class if a given method is not modifying any member then you always tend to put a const keyword in the end.
#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.
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. All constexpr variables are const .
Asserting that something can be computed at compile-time is a pretty strong kind of optimization.
Inlining merely removes a function call, by copy/pasting the function body into the call site. The function body still has to be executed, you just save the overhead of a function call.
But if you make the same code be evaluated at compile-time, it is free at runtime.
But neither inline nor constexpr are primarily about optimization. inline's main purpose is to suppress the one-definition-rule, so that functions can be defined in headers (which is useful for templates, and incidentally, also makes the inlining optimization easier)
And constexpr is there because it is useful in metaprogramming, and incidentally, it may help the compiler better optimize the code, by moving more computations to compile-time.
180
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
