I am working on documenting a new and expanded Lua API for the game Bitfighter (http://bitfighter.org). Our Lua object model is a subset of the C++ object model, and the methods exposed to Lua that I need to document are a subset of the methods available in C++. I want to document only the items relevant to Lua, and ignore the rest.
For example, the object BfObject is the root of all the Lua objects, but is itself in the middle of the C++ object tree. BfObject has about 40 C++ methods, of which about 10 are relevant to Lua scripters. I wish to have our documentation show BfObject as the root object, and show only those 10 relevant methods. We would also need to show its children objects in a way that made the inheritance of methods clear.
For the moment we can assume that all the code is written in C++.
One idea would be to somehow mark the objects we want to document in a way that a system such as doxygen would know what to look at and ignore the rest. Another would be to preprocess the C++ code in such a way as to delete all the non-relevant bits, and document what remains with something like doxygen. (I actually got pretty far with this approach using luadoc, but could not find a way to make luadoc show object hierarchy.)
One thing that might prove helpful is that every Lua object class is registered in a consistent manner, along with its parent class.
There are a growing number of games out there that use Lua for scripting, and many of them have decent documentation. Does anyone have a good suggestion on how to produce it?
PS To clarify, I'm happy to use any tool that will do the job -- doxygen and luadoc are just examples that I am somewhat familiar with.
I have found a solution, which, while not ideal, works pretty well. I cobbled together a Perl script which rips through all the Bitfighter source code and produces a second set of "fake" source that contains only the elements I want. I can then run this secondary source through Doxygen and get a result that is 95% of what I'm looking for.
I'm declaring victory.
One advantage of this approach is that I can document the code in a "natural" way, and don't need to worry about marking what's in and what's out. The script is smart enough to figure it out from the code structure.
If anyone is interested, the Perl script is available in the Bitfighter source archive at https://code.google.com/p/bitfighter/source/browse/luadoc.pl. It is only about 80% complete, and is missing a few very important items (such as properly displaying function args), but the structure is there, and I am satisfied the process will work. The script will improve with time.
The (very preliminary) results of the process can be seen at http://bitfighter.org/luadocs/index.html. The templates have hardly been modified, so it has a very "stock" look, but it shows that things more-or-less work.
Since some commenters have suggested that it is impossible to generate good documentation with Doxygen, I should note that almost none of our inline docs have been added yet. To get a sense of what they will look like, see the Teleporter class. It's not super good, but I think it does refute the notion that Doxygen always produces useless docs.
My major regret at this point is that my solution is really a one-off and does not address what I think is a growing need in the community. Perhaps at some point we'll standardize on a way of merging C++ and Lua and the task of creating a generalized documentation tool will be more manageable.
PS You can see what the markup in the original source files looks like... see https://code.google.com/p/bitfighter/source/browse/zap/teleporter.cpp, and search for #luaclass
Exclude either by namespace (could be class as well) of your C++ code, but not the lua code
EXCLUDE_SYMBOLS = myhier_cpp::*
in the doxygen config file or cherry pick what to exclude by using
/// #cond
class aaa {
...
...
}
/// #endcond
in your c++ code.
I personally think that separating by namespace is better since it reflects the separation in code + documentation, which leads to a namespace based scheme for separation of pure c++ from lua bindings.
Separating via exclusion is probably the most targeted approach but that would involve an extra tool to parse the code, mark up relevant lua parts and add the exclusion to the code. (Additionally you could also render special info like graphs separately with this markup and add them via an Image to your documentation, at least that's easy to do with Doxygen.). Since there has to be some kind of indication of lua code, the markup is probably not too difficult to derive.
Another solution is to use LDoc. It also allows you to write C++ comments, which will be parsed by LDoc and included into the documentation.
An advantage is that you can just the same tool to document your lua code as well. A drawback is that the project seems to be unmaintained. It may also not be possible to document complex object hierarchies, like the questioner mentioned.
I forked it myself for some small adjustments regarding c++. Have a look here.
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C++ code dependency / call-graph “viewer”?
I am working on a huge C++ code base and currently I am stuck with the problem of modularizing my code. I have to divide my code into separate independent modules.
One approach I can think of is to generate the dependency graph and then do a higher level categorization. Other approach is to start with a entry point (some function abc()) and generating a function call tree whose each node will contain the name of the file in which that function resides. Thereafter I can use some script to extract those functions into separate modules.
My question is, is there any tool that can help me do this task? Has anybody faced such a problem earlier. Or can you suggest any approach to achieve the same?
First level of modularization - and I hope you already have done that - is structuring your code in classes. If your code is merely a collection of functions - i.e., C plus some syntactic suggar - then it's high time to rewrite your code, because no amount of dependency-graph-building will save you from maintenance hell.
If you have classes, modularizing should be a matter of finding classes that closely work together (like Customer, Order and Invoice) and separate them from classes that are only losely coupled with them (like Employer or Facility). Then take it from there.
Modularizing code is something that requires, first and foremost, thought. No automatic procedure is a replacement for that. Actually, from what little you wrote, I would fear that any automated process would make things worse, because apparently there has been too little thought invested in this project already. I.e., you wrote 1 million lines of code without thinking about modularization, and now you want modularization to happen while still not actually thinking about it. You are heading for epic fail.
To get some overview doxygen might help. But you have to play around a little with the doxyfile settings to generate dependency graps and if your Code base is huge you should disable dynamic stuff from the generated methods.
Doxygen can create include, inheritance, call and caller graphs using graphviz.
Here are simple examples but it also works for bigger ones.
But doxygen will only give you an overview and no refactoring capabilities.
I regularly use "Understand for C/C++" to investigate these kind of dependencies.
If the code base is really huge and you start your modularization from scratch, you might want to look at some other tools, like:
Cytoscape (which can take the output of "Understand for C/C++" to visualize the dependencies
Lattix
It sounds like you are looking for a refactoring tool. Try taking a look at the answers on this question: Is there a working C++ refactoring tool?
One method will be a bit long but what you can do is to remove a method and compile to find dependencies and than group the decadencies into one component. Although this does not resolve your issue fully but it is an approach to start off with.
Should all C++ code in a project be encapsulated into a single class with main simply calling that class? Or should the main function declare variables and classes.
If you are going to build a large project in C++, you should at the very least read Large Scale C++ Software Design by John Lakos about it. It's a little old but it sounds like you could benefit from the fundamentals in it.
Keep in mind that building a large scale system in any language is a challenge and requires skill and discipline to prevent it falling to pieces very quickly. Don't take it lightly.
That said, if your definition of "large" is different than mine then I may have alternative advice to give you. I'm assuming you're talking about a project where the word "million" will be mentioned in sentences that also contain the words "lines of code".
for large C++ projects, you should create many classes!
main should just kick things off (maybe doing a few housekeeping things) and then calling into a class that will fire up the rest of the system
If it's a class that really makes sense, sure -- but at least IME, that's a fairly rare exception, not the general rule.
Here, I'm presuming that you don't really mean all the code is in one class, but that there's a single top-level class, so essentially all main does is instantiate and use it. That class, in turn, will presumably instantiate and use other subordinate classes.
If you really mean "should all the code being contained in a single class?", then the answer is almost certainly a resounding "no", except for truly minuscule projects. Much of the design of classes in C++ (and most other OO languages) is completely pointless if all the code is in one class.
If you can put your entire project in one class without going insane, your definition of "large" may be different than most people's here. Which is fine -- just keep in mind when you ask people about a "large" c++ project, they will assume you're talking about something that takes multiple person-years to create.
That said, the same principles of encapsulation apply no matter what the size of the project. Break your logic and data into units that make sense and are not too tied together and then organize your class(es) around those divisions. Don't be afraid to try one organization and then refactor it into another organization if you find yourself copy-pasting code, or if you find one class depending too heavily on another. (Or if you find yourself with too many classes and you're creating many objects to accomplish one task where a single object would be cleaner and easier on you.)
Have fun and don't be afraid to experiment a little.
In C++ you should avoid putting entire project in one class, irrespective of big or small. At the max you can try putting it in 1 or 2 namespace (which can be split across the files).
The advantage of having multiple classes are,
Better maintainability of your code
Putting classes in multiple .h and .cpp files (i.e. small modules) help you fast debugging
If all code is in one class and changes are made somewhere then one has to compile whole project. Instead, if project is across modules, one can just compile the module where changes are made. It saves time a lot.
No! Each header/implementation file pair should represent a single class. Placing a large project in one file is a surefire way to disaster: the project become unmaintainable and compiling will take ages. Break up your code in to appropriately sized pieces.
The main function should not declare the classes, rather, the file it contains (often named something like main.cpp, driver.cpp, projectname.cpp) should use #include directives to make the compiler read the declarations in header files. Read up on C++'s separate compilation model for more info.
Some newcomers to C++ find the compilation model - as well as error codes generated when you screw it up - incomprehensible or intimidating and give up thinking it's not worth it. Don't let this be you. Learn how to properly organize your code.
So we have this huge (is 11000 lines huge?) mainmodule.cpp source file in our project and every time I have to touch it I cringe.
As this file is so central and large, it keeps accumulating more and more code and I can't think of a good way to make it actually start to shrink.
The file is used and actively changed in several (> 10) maintenance versions of our product and so it is really hard to refactor it. If I were to "simply" split it up, say for a start, into 3 files, then merging back changes from maintenance versions will become a nightmare. And also if you split up a file with such a long and rich history, tracking and checking old changes in the SCC history suddenly becomes a lot harder.
The file basically contains the "main class" (main internal work dispatching and coordination) of our program, so every time a feature is added, it also affects this file and every time it grows. :-(
What would you do in this situation? Any ideas on how to move new features to a separate source file without messing up the SCC workflow?
(Note on the tools: We use C++ with Visual Studio; We use AccuRev as SCC but I think the type of SCC doesn't really matter here; We use Araxis Merge to do actual comparison and merging of files)
Merging will not be such a big nightmare as it will be when you'll get 30000 LOC file in the future. So:
Stop adding more code to that file.
Split it.
If you can't just stop coding during refactoring process, you could leave this big file as is for a while at least without adding more code to it: since it contains one "main class" you could inherit from it and keep inherited class(es) with overloaded functions in several new small and well designed files.
Find some code in the file which is relatively stable (not changing fast, and doesn't vary much between branches) and could stand as an independent unit. Move this into its own file, and for that matter into its own class, in all branches. Because it's stable, this won't cause (many) "awkward" merges that have to be applied to a different file from the one they were originally made on, when you merge the change from one branch to another. Repeat.
Find some code in the file which basically only applies to a small number of branches, and could stand alone. Doesn't matter whether it's changing fast or not, because of the small number of branches. Move this into its own classes and files. Repeat.
So, we've got rid of the code that's the same everywhere, and the code that's specific to certain branches.
This leaves you with a nucleus of badly-managed code - it's needed everywhere, but it's different in every branch (and/or it changes constantly so that some branches are running behind others), and yet it's in a single file that you're unsuccessfully trying to merge between branches. Stop doing that. Branch the file permanently, perhaps by renaming it in each branch. It's not "main" any more, it's "main for configuration X". OK, so you lose the ability to apply the same change to multiple branches by merging, but this is in any case the core of code where merging doesn't work very well. If you're having to manually manage the merges anyway to deal with conflicts, then it's no loss to manually apply them independently on each branch.
I think you're wrong to say that the kind of SCC doesn't matter, because for example git's merging abilities are probably better than the merge tool you're using. So the core problem, "merging is difficult" occurs at different times for different SCCs. However, you're unlikely to be able to change SCCs, so the issue is probably irrelevant.
It sounds to me like you're facing a number of code smells here. First of all the main class appears to violate the open/closed principle. It also sounds like it is handling too many responsibilities. Due to this I would assume the code to be more brittle than it needs to be.
While I can understand your concerns regarding traceability following a refactoring, I would expect that this class is rather hard to maintain and enhance and that any changes you do make are likely to cause side effects. I would assume that the cost of these outweighs the cost of refactoring the class.
In any case, since the code smells will only get worse with time, at least at some point the cost of these will outweigh the cost of refactoring. From your description I would assume that you're past the tipping point.
Refactoring this should be done in small steps. If possible add automated tests to verify current behavior before refactoring anything. Then pick out small areas of isolated functionality and extract these as types in order to delegate the responsibility.
In any case, it sounds like a major project, so good luck :)
The only solution I have ever imagined to such problems follows. The actual gain by the described method is progressiveness of the evolutions. No revolutions here, otherwise you'll be in trouble very fast.
Insert a new cpp class above the original main class. For now, it would basically redirect all calls to the current main class, but aim at making the API of this new class as clear and succinct as possible.
Once this has been done, you get the possibility to add new functionalities in new classes.
As for existing functionalities, you have to progressively move them in new classes as they become stable enough. You will lose SCC help for this piece of code, but there is not much that can be done about that. Just pick the right timing.
I know this is not perfect, though I hope it can help, and the process must be adapted to your needs!
Additional information
Note that Git is an SCC that can follow pieces of code from one file to another. I have heard good things about it, so it could help while you are progressively moving your work.
Git is constructed around the notion of blobs which, if I understand correctly, represent pieces of code files. Move these pieces around in different files and Git will find them, even if you modify them. Apart from the video from Linus Torvalds mentioned in comments below, I have not been able to find something clear about this.
Confucius say: "first step to getting out of hole is to stop digging hole."
Let me guess: Ten clients with divergent feature sets and a sales manager that promotes "customization"? I've worked on products like that before. We had essentially the same problem.
You recognize that having an enormous file is trouble, but even more trouble is ten versions that you have to keep "current". That's multiple maintenance. SCC can make that easier, but it can't make it right.
Before you try to break the file into parts, you need to bring the ten branches back in sync with each other so that you can see and shape all the code at once. You can do this one branch at a time, testing both branches against the same main code file. To enforce the custom behavior, you can use #ifdef and friends, but it's better as much as possible to use ordinary if/else against defined constants. This way, your compiler will verify all types and most probably eliminate "dead" object code anyway. (You may want to turn off the warning about dead code, though.)
Once there's only one version of that file shared implicitly by all branches, then it's rather easier to begin traditional refactoring methods.
The #ifdefs are primarily better for sections where the affected code only makes sense in the context of other per-branch customizations. One may argue that these also present an opportunity for the same branch-merging scheme, but don't go hog-wild. One colossal project at a time, please.
In the short run, the file will appear to grow. This is OK. What you're doing is bringing things together that need to be together. Afterwards, you'll begin to see areas that are clearly the same regardless of version; these can be left alone or refactored at will. Other areas will clearly differ depending on the version. You have a number of options in this case. One method is to delegate the differences to per-version strategy objects. Another is to derive client versions from a common abstract class. But none of these transformations are possible as long as you have ten "tips" of development in different branches.
I don't know if this solves your problem, but what I guess you want to do is migrate the content of the file to smaller files independent of each other (summed up).
What I also get is that you have about 10 different versions of the software floating around and you need to support them all without messing things up.
First of all there is just no way that this is easy and will solve itself in a few minutes of brainstorming. The functions linked in your file are all vital to your application, and simply cutting them of and migrating them to other files won't save your problem.
I think you only have these options:
Don't migrate and stay with what you have. Possibly quit your job and start working on serious software with good design in addition. Extreme programming is not always the best solution if you are working on a long time project with enough funds to survive a crash or two.
Work out a layout of how you would love your file to look once it's split up. Create the necessary files and integrate them in your application. Rename the functions or overload them to take an additional parameter (maybe just a simple boolean?).
Once you have to work on your code, migrate the functions you need to work on to the new file and map the function calls of the old functions to the new functions.
You should still have your main-file this way, and still be able to see the changes that were made to it, once it comes to a specific function you know exactly when it was outsourced and so on.
Try to convince your co-workers with some good cake that workflow is overrated and that you need to rewrite some parts of the application in order to do serious business.
Exactly this problem is handled in one of the chapters of the book "Working Effectively with Legacy Code" (http://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052).
I think you would be best off creating a set of command classes that map to the API points of the mainmodule.cpp.
Once they are in place, you will need to refactor the existing code base to access these API points via the command classes, once that's done, you are free to refactor each command's implementation into a new class structure.
Of course, with a single class of 11 KLOC the code in there is probably highly coupled and brittle, but creating individual command classes will help much more than any other proxy/facade strategy.
I don't envy the task, but as time goes on this problem will only get worse if it's not tackled.
Update
I'd suggest that the Command pattern is preferable to a Facade.
Maintaining/organizing a lot of different Command classes over a (relatively) monolithic Facade is preferable. Mapping a single Facade onto a 11 KLOC file will probably need to be broken up into a few different groups itself.
Why bother trying to figure out these facade groups? With the Command pattern you will be able to group and organise these small classes organically, so you have a lot more flexibility.
Of course, both options are better than the single 11 KLOC and growing, file.
One important advice: Do not mix refactoring and bugfixes. What you want is a Version of your program that is identical to the previous version, except that the source code is differently.
One way could be to start splitting up the least big function/part into it's own file and then either include with a header (thus turning main.cpp into a list of #includes, which sounds a code smell in itself *I'm not a C++ Guru though), but at least it's now split into files).
You could then try to switch all maintenance releases over to the "new" main.cpp or whatever your structure is. Again: No other changes or Bugfixes because tracking those is confusing as hell.
Another thing: As much as you may desire making one big pass at refactoring the whole thing in one go, you might bite off more than you can chew. Maybe just pick one or two "parts", get them into all the releases, then add some more value for your customer (after all, Refactoring does not add direct value so it is a cost that has to be justified) and then pick another one or two parts.
Obviously that requires some discipline in the team to actually use the split files and not just add new stuff to the main.cpp all the time, but again, trying to do one massive refactor may not be the best course of action.
Rofl, this reminds me of my old job. It seems that, before I joined, everything was inside one huge file (also C++). Then they've split it up (at completely random points using includes) into about three (still huge files). The quality of this software was, as you might expect, horrible. The project totaled at about 40k LOC. (containing almost no comments but LOTS of duplicate code)
In the end I did a complete rewrite of the project. I started by redoing the worst part of the project from scratch. Of course I had in mind a possible (small) interface between this new part and the rest. Then I did insert this part into the old project. I didn't refactor the old code to create the interface necessary, but just replaced it. Then I took made small steps from there, rewriting the old code.
I have to say that this took about half a year and there was no development of the old code base beside bugfixes during that time.
edit:
The size stayed at about 40k LOC but the new application contained many more features and presumably less bugs in its initial version than the 8 year old software. One reason of the rewrite was also that we needed the new features and introducing them inside the old code was nearly impossible.
The software was for an embedded system, a label printer.
Another point that I should add is that in theory the project was C++. But it wasn't OO at all, it could have been C. The new version was object oriented.
OK so for the most part rewriting API of production code is a bad idea as a start. Two things need to happen.
One, you need to actually have your team decide to do a code freeze on current production version of this file.
Two, you need to take this production version and create a branch that manages the builds using preprocessing directives to split up the big file. Splitting the compilation using JUST preprocessor directives (#ifdefs, #includes, #endifs) is easier than recoding the API. It's definitely easier for your SLAs and ongoing support.
Here you could simply cut out functions that relate to a particular subsystem within the class and put them in a file say mainloop_foostuff.cpp and include it in mainloop.cpp at the right location.
OR
A more time consuming but robust way would be to devise an internal dependencies structure with double-indirection in how things get included. This will allow you to split things up and still take care of co-dependencies. Note that this approach requires positional coding and therefore should be coupled with appropriate comments.
This approach would include components that get used based on which variant you are compiling.
The basic structure is that your mainclass.cpp will include a new file called MainClassComponents.cpp after a block of statements like the following:
#if VARIANT == 1
# define Uses_Component_1
# define Uses_Component_2
#elif VARIANT == 2
# define Uses_Component_1
# define Uses_Component_3
# define Uses_Component_6
...
#endif
#include "MainClassComponents.cpp"
The primary structure of the MainClassComponents.cpp file would be there to work out dependencies within the sub components like this:
#ifndef _MainClassComponents_cpp
#define _MainClassComponents_cpp
/* dependencies declarations */
#if defined(Activate_Component_1)
#define _REQUIRES_COMPONENT_1
#define _REQUIRES_COMPONENT_3 /* you also need component 3 for component 1 */
#endif
#if defined(Activate_Component_2)
#define _REQUIRES_COMPONENT_2
#define _REQUIRES_COMPONENT_15 /* you also need component 15 for this component */
#endif
/* later on in the header */
#ifdef _REQUIRES_COMPONENT_1
#include "component_1.cpp"
#endif
#ifdef _REQUIRES_COMPONENT_2
#include "component_2.cpp"
#endif
#ifdef _REQUIRES_COMPONENT_3
#include "component_3.cpp"
#endif
#endif /* _MainClassComponents_h */
And now for each component you create a component_xx.cpp file.
Of course i am using numbers but you should use something more logical based on your code.
Using preprocessor allows you to split things up without having to worry about API changes which is a nightmare in production.
Once you have production settled you can then actually work on redesign.
Well I understand your pain :) I've been in a few such projects as well and it's not pretty. There is no easy answer for this.
One approach that may work for you is to start adding safe guards in all functions, that is, checking arguments, pre/post-conditions in methods, then eventually adding unit tests all in order to capture the current functionality of the sources. Once you have this you are better equipped to re-factor the code because you will have asserts and errors popping up alerting you if you have forgotten something.
Sometimes though there are times when refactoring just may bring more pain than benefit. Then it may be better to just leave the original project and in a pseudo maintenance state and start from scratch and then incrementally adding the functionality from the beast.
You should not be concerned with reducing the file-size, but rather with reducing the class-size. It comes down to almost the same, but makes you look at the problem from a different angle (as #Brian Rasmussen suggests, your class seems to have to many responsibilities).
What you have is a classic example a known design antipattern called the blob. Take some time to read the article I point here, and maybe you may find something useful. Besides, if this project is as big as it looks, you should consider some design to prevent growing into code that you can't control.
This isn't an answer to the big problem, but a theoretical solution to a specific piece of it:
Figure out where you want to split the big file into subfiles. Put comments in some special format at each of those points.
Write a fairly trivial script that will break the file apart into subfiles at those points. (Perhaps the special comments have embedded filenames that the script can use as instructions for how to split it.) It should preserve the comments as part of the splitting.
Run the script. Delete the original file.
When you need to merge from a branch, first recreate the big file by concatenating the pieces back together, do the merge, and then re-split it.
Also, if you want to preserve the SCC file history, I expect the best way to do that is to tell your source control system that the individual piece files are copies of the original. Then it will preserve the history of the sections that were kept in that file, although of course it will also record that large parts were "deleted".
One way to split it without too much danger would be to take a historic look at all the line changes. Are there certain functions that are more stable than others? Hot spots of change if you will.
If a line hasn't been changed in a few years you can probably move it to another file without too much worry. I'd take a look at the source annotated with the last revision that touched a given line and see if there are any functions you could pull out.
Wow, sounds great. I think explaining to your boss, that you need a lot of time to refactor the beast is worth a try. If he doesn't agree, quitting is an option.
Anyway, what I suggest is basically throwing out all the implementation and regrouping it into new modules, let's call those "global services". The "main module" would only forward to those services and ANY new code you write will use them instead of the "main module". This should be feasible in a reasonable amount of time (because it's mostly copy and paste), you don't break existing code and you can do it one maintenance version at a time. And if you still have any time left, you can spend it refactoring all old depending modules to also use the global services.
Do not ever touch this file and the code again!
Treat is like something you are stuck with. Start writing adapters for the functionality encoded there.
Write new code in different units and talk only to adapters which encapsulate the functionality of the monster.
... if only one of the above is not possible, quit the job and get you a new one.
My sympathies - in my previous job I encountered a similar situation with a file that was several times larger than the one you have to deal with. Solution was:
Write code to exhaustively test the function in the program in question. Sounds like you won't already have this in hand...
Identify some code that can be abstracted out into a helper/utilities class. Need not be big, just something that is not truly part of your 'main' class.
Refactor the code identified in 2. into a separate class.
Rerun your tests to ensure nothing got broken.
When you have time, goto 2. and repeat as required to make the code manageable.
The classes you build in step 3. iterations will likely grow to absorb more code that is appropriate to their newly-clear function.
I could also add:
0: buy Michael Feathers' book on working with legacy code
Unfortunately this type of work is all too common, but my experience is that there is great value in being able to make working but horrid code incrementally less horrid while keeping it working.
Consider ways to rewrite the entire application in a more sensible way. Maybe rewrite a small section of it as a prototype to see if your idea is feasible.
If you've identified a workable solution, refactor the application accordingly.
If all attempts to produce a more rational architecture fail, then at least you know the solution is probably in redefining the program's functionality.
My 0.05 eurocents:
Re-design the whole mess, split it into subsystems taking into account the technical and business requirements (=many parallel maintenance tracks with potentially different codebase for each, there is obviously a need for high modifiability, etc.).
When splitting into subsystems, analyze the places which have most changed and separate those from the unchanging parts. This should show you the trouble-spots. Separate the most changing parts to their own modules (e.g. dll) in such a way that the module API can be kept intact and you don't need to break BC all the time. This way you can deploy different versions of the module for different maintenance branches, if needed, while having the core unchanged.
The redesign will likely need to be a separate project, trying to do it to a moving target will not work.
As for the source code history, my opinion: forget it for the new code. But keep the history somewhere so you can check it, if needed. I bet you won't need it that much after the beginning.
You most likely need to get management buy-in for this project. You can argue perhaps with faster development time, less bugs, easier maintaining and less overall chaos. Something along the lines of "Proactively enable the future-proofness and maintenance viability of our critical software assets" :)
This is how I'd start to tackle the problem at least.
Start by adding comments to it. With reference to where functions are called and if you can move things around. This can get things moving. You really need to assess how brittle the code base it. Then move common bits of functionality together. Small changes at a time.
Another book you may find interesting/helpful is Refactoring.
Something I find useful to do (and I'm doing it now although not at the scale you face), is to extract methods as classes (method object refactoring). The methods that differ across your different versions will become different classes which can be injected into a common base to provide the different behaviour you need.
I found this sentence to be the most interesting part of your post:
> The file is used and actively changed in several (> 10) maintenance versions of our product and so it is really hard to refactor it
First, I would recommend that you use a source control system for developing these 10 + maintenance versions that supports branching.
Second, I would create ten branches (one for each of your maintenance versions).
I can feel you cringing already! But either your source control isn't working for your situation because of a lack of features, or it's not being used correctly.
Now to the branch you work on - refactor it as you see fit, safe in the knowledge that you'll not upset the other nine branches of your product.
I would be a bit concerned that you have so much in your main() function.
In any projects I write, I would use main() only perform initialization of core objects - like a simulation or application object - these classes is where the real work should go on.
I would also initialize an application logging object in main for use globally throughout the program.
Finally, in main I also add leak detection code in preprocessor blocks that ensure it's only enabled in DEBUG builds. This is all I would add to main(). Main() should be short!
You say that
> The file basically contains the "main class" (main internal work dispatching and coordination) of our program
It sounds like these two tasks could be split into two separate objects - a co-ordinator and a work dispatcher.
When you split these up, you may mess up your "SCC workflow", but it sounds like adhering stringently to your SCC workflow is causing software maintenance problems. Ditch it, now and don't look back, because as soon as you fix it, you'll begin to sleep easy.
If you're not able to make the decision, fight tooth and nail with your manager for it - your application needs to be refactored - and badly by the sounds of it! Don't take no for an answer!
As you've described it, the main issue is diffing pre-split vs post-split, merging in bug fixes etc.. Tool around it. It won't take that long to hardcode a script in Perl, Ruby, etc. to rip out most of the noise from diffing pre-split against a concatenation of post-split. Do whatever's easiest in terms of handling noise:
remove certain lines pre/during concatenation (e.g. include guards)
remove other stuff from the diff output if necessary
You could even make it so whenever there's a checkin, the concatenation runs and you've got something prepared to diff against the single-file versions.
"The file basically contains the "main class" (main internal work dispatching and coordination) of our program, so every time a feature is added, it also affects this file and every time it grows."
If that big SWITCH (which I think there is) becomes the main maintenance problem, you could refactor it to use dictionary and the Command pattern and remove all switch logic from the existing code to the loader, which populates that map, i.e.:
// declaration
std::map<ID, ICommand*> dispatchTable;
...
// populating using some loader
dispatchTable[id] = concreteCommand;
...
// using
dispatchTable[id]->Execute();
I think the easiest way to track the history of source when splitting a file would be something like this:
Make copies of the original source code, using whatever history-preserving copy commands your SCM system provides. You'll probably need to submit at this point, but there's no need yet to tell your build system about the new files, so that should be ok.
Delete code from these copies. That should not break the history for the lines you keep.
I think what I would do in this situation is bit the bullet and:
Figure out how I wanted to split the file up (based on the current development version)
Put an administrative lock on the file ("Nobody touch mainmodule.cpp after 5pm Friday!!!"
Spend your long weekend applying that change to the >10 maintenance versions (from oldest to newest), up to and including the current version.
Delete mainmodule.cpp from all supported versions of the software. It's a new Age - there is no more mainmodule.cpp.
Convince Management that you shouldn't be supporting more than one maintenance version of the software (at least without a big $$$ support contract). If each of your customers have their own unique version.... yeeeeeshhhh. I'd be adding compiler directives rather than trying to maintain 10+ forks.
Tracking old changes to the file is simply solved by your first check-in comment saying something like "split from mainmodule.cpp". If you need to go back to something recent, most people will remember the change, if it's 2 year from now, the comment will tell them where to look. Of course, how valuable will it be to go back more than 2 years to look at who changed the code and why?