(""); } constexpr std::size_t size() const { return sz; } }; // C++11 constexpr functions had to put everything in a single return statement // (C++14 doesn't have that requirement) constexpr std::size_t countl
// OK, constexpr functions can be evaluated at compile time // and used in contexts that require constant expressions. int array[array_size2(10)]; struct S { S() { } constexpr S(int) { } constexpr virtual int f() { // Error, f must not be virtual. return 55; } }; struct ...
When a function template is declared as aconstexprfunction, if the instantiation results in a function that does not satisfy the requirements of aconstexprfunction, theconstexprspecifier is ignored. For example: template <class C> constexpr NL f6(C c) { // OK, the constexpr specifier ignore...
Always test your constexpr functions in a constant context, as they may work when called in a non-constant context but fail in a constant context. When should I constexpr a function? As a general rule, if a function can be evaluated as part of a required constant expression, it should ...
a normal function, computing its result at runtime.This means you don't need two functions to ...
constexpr functions in C++14 are pretty comfortable. They can invoke otherconstexprfunctions. can have variables that have to be initialized by a constant expression. can have conditional expressions or loops. are implicitinline. cannot havestaticorthread_localdata. ...
在前面提到,用include static functions的方式中include进来的函数体可能不完全一样。inline此处也提到,你要是同名函数的函数体长得不一样,我才不告诉你我要留哪一份删哪几份呢。你要是敢这么做,我不保证我的输出有意义。这个在C++里叫做ODR violation (Definitions and ODR)。编译器一次只看一个translation unit...
定义:constexpr用于定义在编译期可求值的常量表达式。 示例: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 constexpr int x=5; 这里,x的值在编译期就确定为5。 const 定义:const表示变量在运行期间不能被修改,但不保证在编译期求值。 示例:
The following example showsconstexprvariables, functions, and a user-defined type. In the last statement inmain(), theconstexprmember functionGetValue()is a run-time call because the value isn't required to be known at compile time.
Fast forward to C++20, we have another keyword:consteval. This time it can be applied only to functions and forces all calls to happen at compile time. For example: constevalintsum(inta,intb){returna+b;}constexprintsum_c(inta,intb){returna+b;}intmain(){constexprautoc=sum(100,100);...