C++ inline member function in .cpp file

Question

I know that inline member functions by definition should go into the header. But what if it's not possible to put the implementation of the function into the header? Let's take this situation:

File A.h

#pragma once #include "B.h"  class A{     B b; }; 

File B.h

#pragma once  class A; //forward declaration  class B{     inline A getA(); }; 

Due to the circular include I have to put the implementation of getA into

B.cpp

#include "B.h" #include "A.h"  inline A B::getA(){     return A(); } 

Will the compiler inline getA? If so, which inline keyword is the significant one (the one in the header or the one in the .cpp file)? Is there another way to put the definition of an inline member function into its .cpp file?

Answer 1

Quoting from C++ FAQ:

Note: It's imperative that the function's definition (the part between the {...}) be placed in a header file, unless the function is used only in a single .cpp file. In particular, if you put the inline function's definition into a .cpp file and you call it from some other .cpp file, you'll get an "unresolved external" error from the linker.

The compiler need to see the definition of the inline function whenever it finds any use of that inline function. That is typically possible if the inline function is placed in a header file.

Will the compiler inline getA?

No, except when the the use of getA() is in B.cpp itself.

If so, which inline keyword is the significant one (the one in the header or the one in the cpp)?

Best practice: only in the definition outside the class body.

Is there another way to put the definition of an inline member function into it's cpp file?

No, at least I don't know.