template<int> struct X {}; constexpr auto f() { int const N = std::is_constant_evaluated() ? 13 : 17; X<N> x1; X<std::is_constant_evaluated() ? 13 : 17> x2; } 我们希望上面的x1和x2有着相同的类型,但是N的初始化并不要求一个常量值(请注意:const只是表明一个不可变值,不是...
inty;constinta=std::is_constant_evaluated()?y:1;// 试探性常量求值失败,常量求值被舍弃。// 变量 a 动态初始化为 1constintb=std::is_constant_evaluated()?2:y;// 常量求值(std::is_constant_evaluation() == true)成功。// 变量 b 静态初始化为 2 ...
例如，GCC在is_constant_evaluated之前使用__builtin_constant_p。演示：GCC 6.1 running C++17 ...
We remember that we calledis_constant_evaluatedin the array bound and memoized its value. This would be a reasonable design but the outcome is that code is a VLA which is UB. Not helpful in this specific case When constant folding in an array,is_constant_evaluatedis true (the context can...
. I played a little bit with it, and I realized it is somewhat tricky. Here’s my test: constexpr int Fn1() { if constexpr (std::is_constant_evaluated()) return 0; else return 1; } constexpr int Fn2() { if (std::is_constant_evaluated()) return 0; else return 1; } int ...
#include <type_traits> struct X { static const int x = 1/(1-std::is_constant_evaluated()); }; int z[X::x]; gcc and MSVC correctly error; clang somehow evaluates it to 1. It looks like clang somehow falls back on non-constant-context evaluation in some cases. github-actions bot...
__cpp_lib_is_constant_evaluated201811L(C++20)std::is_constant_evaluated Example Run this code #include <cmath>#include <iostream>#include <type_traits>constexprdoublepower(doubleb,intx){if(std::is_constant_evaluated()&&!(b==0.0&&x<0)){// A constant-evaluation context: Use a constexpr...
Here the 'context' variable is always 'false'. The code becomes unreachable as early as the 'then' branch. The 'std::is_constant_evaluated' always returns 'true' if called in one of the following locations: inside 'static_assert'; inside the 'consteval' function; inside the 'if constexp...
__builtin_is_constant_evaluated是用于在clang和gcc标准库中实现std::is_constant_evaluated的内置组件。例如: if (__builtin_is_constant_evaluated()) else { int我知道这将使__builtin_is_constant_evaluated()实现的返回值得到定义,因为优化在不同编译器之间有所不同。但是,只有当两条路径具有相 浏览0提问...
在C++20中,std::indirect_result_t 是一种类型别名模板,用于表示一个可调用对象的返回类型。它被用于定义 C++20 中的协程和范式编程的操作符 co_await 和co_yield。 std::indirect_result_t 的定义如下: 代码语言:txt 复制 template <typename Fn, typename... Args> using indirect_result_t = decltype(s...