constexpr vs define | What's the difference between constexpr and const?

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constexpr vs define*******#define directives create macro substitution, while constexpr variables are special type of variables. They literally have nothing in common beside the fact that before constexpr (or even const) variables were available, macros were sometimes used . constexpr declares an object as fit for use in what the Standard calls constant expressions. But note that constexpr is not the only way to do this. When .

Constexpr vs #define: A Comparison of Two C++ Language FeaturesWhat's the difference between constexpr and const?Constexpr vs #define: A Comparison of Two C++ Language Featuresconstexpr vs defineconstexpr (C++) | Microsoft Learnconstexpr (C++) | Microsoft Learn

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. .

A constexpr specifier used in a function or static data member(since C++17) declaration implies inline. If any declaration of a function or function template has a . Compile-time Evaluation. One of the key advantages of constexpr is its ability to perform computations at compile-time. This means that expressions marked as .

Let’s compare them in this article. const vs constexpr const, our good old fried from the early days of C++ (and also C), can be applied to objects to indicate immutability. As of C++20, we have four keywords beginning with const. . Defines an expression that can be evaluated at compile time. Such expressions can be used as non .

Constexpr is often compared to the preprocessor feature #define in C++, as both can be used to define constants in code. However, there are some key differences between the two. Compile-time vs Preprocessing: Constexpr allows for compile-time evaluation of expressions, while #define is a preprocessor directive that performs text .

constexpr関数はコンパイル時でも実行時でも使える。 ここで疑問 Question. templateが型安全なのに、なぜ今だにdefineを使うのか？ Answer. defineでしかできないことがある。 defineにしかできないこと ①シンボル定義. 変数名を変えることができる。 ##がキモIn C++17, the proper way to replace those old idioms (e.g. #define) in headers in namespace scope is to use constexpr inline variables -- and not static (which is implied: they already have internal linkage). While typically you won't encounter ODR issues (because integer compile-time constants such as those you describe are rarely ODR . I have seen many arduino programs with many, many #define constants that should be using c++'s constexpr. Read here: c++ - Constexpr vs macros - Stack Overflow There should be a page about how to use constexpr on the arduino refrence, and it should be preferred over #define. Of course, using #define for pre-processor if statements (#if) .What's the Difference? Const and constexpr are both used in C++ to define constants, but they have different purposes. Const is used to declare variables that cannot be modified after initialization, providing read-only access to the variable. Constexpr, on the other hand, is used to define constants that can be evaluated at compile time . C++17 inline variable runnable example. C++17 inline variables were mentioned at: use of constexpr in header file and here is a minimal runnable example that shows that only a single memory location is used: main.cpp. #include #include "notmain.hpp" int main() { // Both files see the same memory address.

3. 为什么Visual Studio建议使用constexpr代替#define. 基于上述的优点，Visual Studio推荐使用constexpr代替宏。具体来说，Visual Studio有一个名为"使用constexpr而非#define"的代码分析规则（C26432），当开发者使用#define定义常量或函数时，它会提出警告，并建议使用constexpr代替。 Most objects declared as constexpr are immutable, but it is possible to define a constexpr object that is (partially) mutable as follows: struct S { mutable int m; }; int main() { constexpr S s{42}; int arr[s.m]; // error: s.m is not a constant expression s.m = 21; // ok, assigning to a mutable member of a const object } . I am trying to replace the preprocessor #define and #if/#ifdef's that I am using to control conditional compilation with constexpr variables and ifs. Is it possible to declare constexpr variables . Photo by Luca Bravo on Unsplash Overview. The constexpr specifier was introduced in C++11, for beginners it is confusing because it is similar to the const qualifier.. constexpr stands for constant expression and is used to specify that a variable or function can be used in a constant expression, an expression that can be evaluated at compile .

constexpr functions are also allowed to be called at runtime. Prerequisites. Here I assume you are familiar with the concept of compile-time vs runtime, auto keyword, and templates. I am using GCC 10.2 and Clang 14 with flag -std=c++20. constexpr values. We can store a compile-time value with constexpr:

With the relatively new keyword constexpr we can do a few good stuff we couldn't with const. E.g: constexpr int GetVal() { return 40; } int arr[GetVal()]; And yeah.there are also many other usages for constexpr, like in constructors..etc. Now the question is, is there any benefit of using it over #define macros? edit

However it makes a difference if you define a constexpr variable in a function static or nonstatic, eg. if a constexpr array is nonstatic, gcc just moves the data with hardcoded mov-instructions onto the stack, while static constexpr just stores the data in . In your current example there is no difference: On variable declarations, constexpr implies const, and a const variable at namespace scope has internal linkage by default (so adding static does not change anything). In C++14, you cannot declare a variable as constexpr and have it have external linkage unless you only ever do this in . constexpr is a new C++11 keyword that rids you of the need to create macros and hardcoded literals. It also guarantees, under certain conditions, that objects undergo static initialization. Danny Kalev shows how to embed constexpr in C++ applications to define constant expressions that might not be so constant otherwise.. . From S. Meyers, Effective Modern C++, Item 15 ("Use constexpr whenever possible"): Things to Remember. constexpr objects are const and are initialized with values known during compilation. [.] constexpr objects and functions may be used in a wider range of contexts than non-constexpr objects and functions.

I tend to prefer the constexpr version, and always use them with templates, but I use the preprocessor version if I need to disable code that won't compile under certain preprocessor definitions. – ChrisMM

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constexpr vs define|What's the difference between constexpr and const?