Question

Is the following free function implicitly inlined in C++, similar to how member functions are implicitly inlined if defined in the class definition?

void func() { ... }

Do template functions behave the same way?

Answer 1

No, it’s not implicitly inlined. The compiler has no way of knowing if another module will use this function, so it has to generate code for it.

This means, for instance, that if you define the function like that in a header and include the header twice, you will get linker errors about multiple definitions. Explicit inline fixes that.

Of course, the compiler may still inline the function if it thinks that will be efficient, but it’s not the same as an explicit inlining.

Template functions are implicitly inlined in the sense that they don’t require an inline to prevent multiple definition errors. I don’t think the compiler is forced to inline those either, but I’m not sure.