c++ - 在 C++ 中声明内联但实际上内联函数是否合法

Question

在头文件中:

inline void func(void); // declare only, with `inline`

在impl源文件中:

void func(void) { balabala(); }

在其他源文件中:

func(); // call the func

问题:声明内联函数是否合法，即使它实际上并未内联在头文件中？

PS:

Why need this: I have some macro generated functions, may or may not be declare in header only, so I wish the macro can be used without explicitly specify inline or not

And, I know the function can be wrapped by a wrapper class as static member function in header

the tricky inline solution was tested under MSVC and clang without compile error, simply want to know whether it's legal in C++ standard

Answer 1

这是不合法的。来自 cppreference.com :

2) The definition of an inline function or variable (since C++17) must be present in the translation unit where it is accessed (not necessarily before the point of access).