I've working on a project at work where there's loads and loads of code in the header files. If I were using Visual Studio this wouldn't be an issue, as this has pre-compiled headers etc, but this is Linux GCC code.
Anyway, its starting to become a bit of an issue with compilation times. Of course the templates are going to have to remain in the headers etc, but most of this code could be extracted into implementation files and linked against as a static library. All of the projects uses these headers and get compiled each time, so it makes sense to create a static lib.
Implementations in the header files are in-lined, or is this only a hint, like the inline keyword? This code is VERY time critical and I'm concerned about moving the implementations out of the headers. Can I achieve the same thing if I use the inline keyword as opposed to having implementations in header files?
** UPDATE ** I know that inline is only a hint to the compiler. I'm not in control of everything in the project and I just want to move everything out of the headers into a library without affecting performance. Is this actually going to be a try it and see thing? I just want to keep performance exactly the same but enhance compile time.
The inline keyword is only a hint to the compiler that it may wish to inline that function. Its real purpose is to allow you to legally "violate" the one definition rule.
In order to inline a function its body has to be visible at the point of call, which typically means that if you move the function to an implentation file it may not be inlined anymore.
But keep in mind that most likely large functions in the header will not be inlined anyway. Also consider that in many cases inlined functions may actually be slower than called functions due to a variety of architecture-specific issues.