c++ - #if 与 if constexpr

Question

哪个更适合编译时配置(例如调试/发布)、预处理器指令或if constexpr？

#define DBG

#if DBG
// some code
#endif

// --------------------------------- or

inline constexpr bool DEBUG { true };

if constexpr ( DEBUG )
{
// some code
}

Answer 1

请注意，如果 if constexpr 不是 模板的一部分，那么 if 的其他部分(例如 elses) 仍然被编译并检查有效性。

来自 cppreference :

If a constexpr if statement appears inside a templated entity, and if condition is not value-dependent after instantiation, the discarded statement is not instantiated when the enclosing template is instantiated .

Outside a template, a discarded statement is fully checked. if constexpr is not a substitute for the #if preprocessing directive: