Inline function v. Macro in C — What's the Overhead (Memory/Speed)?

Question

I searched Stack Overflow for the pros/cons of function-like macros v. inline functions.

I found the following discussion: Pros and Cons of Different macro function

Answer 1

An macro is not really a function. whatever you define as a macro gets verbatim posted into your code, before the compiler gets to see it, by the preprocessor. The preprocessor is just a software engineers tool that enables various abstractions to better structure your code.

A function inline or otherwise the compiler does know about, and can make decisions on what to do with it. A user supplined inline keyword is just a suggestion and the compiler may over-ride it. It is this over-riding that in most cases would result in better code.

Another side effect of the compiler being aware of the functions is that you could potentially force the compiler to take certain decisions -for example, disabling inlining of your code, which could enable you to better debug or profile your code. There are probably many other use-cases that inline functions enable vs. macros.

Macros are extremely powerful though, and to back this up I would cite google test and google mock. There are many reasons to use macros :D.

Simple mathmatical operations that are chained together using functions are often inlined by the compiler, especially if the function is only called once in the translation step. So, I wouldn't be surprised that the compiler takes inlining decisions for you, regardless of weather the keyword is supplied or not.

However, if the compiler doesn't you can manually flatted out segments of your code. If you do flatten it out perhaps macros will serve as a good abstraction, after all they present similar semantics to a "real" function.

The Crux

So, do you want the compiler to be aware of certain logical boundaries so it can produce better physical code, or do you want force decisions on the compiler by flattening it out manually or by using macros. The industry leans towards the former.

I would lean towards using macros in this case, just because it's quick and dirty, without having to learn much more. However, as macros are a software engineering abstraction, and because you are concerned with the code the compiler generates, if the problem were to become slightly more advanced I would use C++ templates, as they were designed for the concerns you are pondering.