Reorganize Classes into Static Libraries

Question

I am about to attempt reorganizing the way my group builds a set of large applications that share about 90% of their source files. Right now, these applications are built without any libraries whatsoever involved except for externally linked ones that are not under our control. The applications use the same common source files (we are not maintaining 5 versions of the same .h/.cpp files), but these are not built into any common library. So, at the moment, we are paying the price of building the same code over-and-over per application, each time we intend to release a version. To me, this sounds like a prime candidate for using libraries to capture the shared code and reduce build times. I do not have the option of using DLL's, so the approach is to use static libraries.

I would like to know what tips you would have for how to approach this task. I have limited experience with creating/organizing static libraries, so even the basic suggestions towards organization/gotchas are welcome. Maybe even a good book recommendation?

I have done a brief exercise by finding the entire subset of files that each application share in common. As a proof of concept, I took these files and placed them in a single "Common Monster" static library. Building the full application using this single static library certainly improves the build time for all of the applications, but should I leave it at this? The purpose of the library in this form is not very focused and seems like a lazy attempt at modularity. There is ongoing development with these applications, and I'm afraid this setup will cause problems further down the line.

Answer 1

It's very hard to give general guidelines in this area - how you structure libraries depends very much on how you use them. Perhaps if I describe my own code libraries this may help:

• One general purpose library containing code that I expect all applications will have at least a 50/50 chance of needing to use. This includes string utilities, regexes, expression evaluation, XML parsing and ODBC support. Conceivably this should be split up a bit, but it makes distributing my code in FOSS projects easier to keep it monolithic.

• A library supporting multi-threading, providing wrappers around threads, mutexes, semaphores etc.

• One supporting SQLite via its native interface, rather than via ODBC.

• A C++ web server wrapper round the Mongoose C web server.

The general purpose library is used in all the stuff I write, the others in more specialised circumstances. Headers for each library are held in separate directories, as are the library binaries themselves (though they should probably be in a single lib directory).

Answer 2

Make sure that the dependencies of your libraries form acyclic directed graph (a tree). While this is not necessarily a problem for static libs (I'm not sure in fact), it will be a problem if you ever decide to switch to dlls. Depending on your situation, this may require some redesign of interfaces.

Another thing I noticed (for sure on MSVC), which you may consider if build speed is an important concern: DLLs link much faster than static libraries. I assume this is because they don't have to be copied into the new executable and there's no need to search an eliminate unused code. Even if it's no option for production, you may use this trick while developing.

I also have the habit to create my solution files with CMake, because it is easier to overview the entire build process than clicking through an endless list of options in a GUI. It's up to you to decide if you want to walk that path.