Two questions about inline functions in C++

Question

I have question when I compile an inline function in C++.

Can a recursive function work with inline. If yes then please describe how.

I am sure about loop

Answer 1

Recursive function can be inlined to certain limited depth of recursion. Some compilers have an option that lets you to specify how deep you want to go when inlining recursive functions. Basically, the compiler "flattens" several nested levels of recursion. If the execution reaches the end of "flattened" code, the code calls itself in usual recursive fashion and so on. Of course, if the depth of recursion is a run-time value, the compiler has to check the corresponding condition every time before executing each original recursive step inside the "flattened" code. In other words, there's nothing too unusual about inlining a recursive function. It is like unrolling a loop. There's no requirement for the parameters to be constant.

What you mean by "I am sure about loop can't work" is not clear. It doesn't seem to make much sense. Functions with a loop can be easily inlined and there's nothing strange about it.

What are you trying to say about your example that "displays nothing" is not clear either. There is nothing in the code that would "display" anything. No wonder it "displays nothing". On top of that, you posted invalid code. C++ language does not allow function declarations without an explicit return type.

As for your last question, yes, the compiler is completely free to implement an inline function as "normal" function. It has nothing to do with function being "too large" though. It has everything to do with more-or-less complex heuristic criteria used by that specific compiler to make the decision about inlining a function. It can take the size into account. It can take other things into account.