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)

+6  A: 

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.

Anders K.
+103  A: 

Merging will not be such a big nightmare as it will be when you'll get 30000 LOC file in the future. So:

  1. Stop adding more code to that file.
  2. 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.

Kirill V. Lyadvinsky
+1 I second that, make a clean break now before doing it later, were it will be even more work...
@Martin: fortunately you haven't pasted your file here, so I have no idea about its structure. But general idea is to split it in logical parts. Such logical parts could contain groups of functions from your "main class" or you could split it in several auxiliary classes.
Kirill V. Lyadvinsky
With 10 maintenance versions and many active developers, it is unlikely the file can be frozen for long enough time.
@Martin, you have a couple of GOF patterns that would do the trick, a single **Facade** that maps the functions of the mainmodule.cpp, alternatively (I've recommended below) create a suite of **Command** classes that each map to a function/feature of (I've expanded on this on my answer.)
Yes totally agree, at some point you have to stop adding code to it or eventually its going to be 30k, 40k, 50k, kaboom mainmodule just seg faulted. :-)
@Kirill: pls spare my browser from 11000 lines of code :P
+42  A: 

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.

A reference on *how* GIT does that / how you do it with GIT would be most welcome.
@Martin Git does it automatically.
@Matthew, Benoit: A link to the GIT docs on which feature you are referring to would still be welcome. I don't seem to able to identify it.
@Martin: Git does it automatically - because it doesn't track files, it tracks content. It is actually more difficult in git to just "get the history of the one file".
@Martin is a talk where Torvalds talks about git. He mentions it later in the talk.
Note: The part about the files-vs-content is at 1:03:00-1:05:30 of the video.
@Martin, look at this question:
+1 for Git, best SCM there is.
Git is great and all, but how would it help him maintain his AccuRev history? That was one of the main points of his question.
To try this, you can use git blame -C -M -w somefile (-w to ignore space difference, -C -M for detecting changes across files relatively aggressively). Sorry for a link to my blog, but I thought it would be easier than giving the full example in comment:
David Cournapeau
+1  A: 

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.

+1 - rewrite it in your own time though otherwise someone might spit their dummy.
+14  A: 

Exactly this problem is handled in one of the chapters of the book "Working Effectively with Legacy Code" (

Patrick makes it possible to see the TOC of this book (and 2 sample chapters). How long is chapter 20? (Just to get a feel of how useful it might be.)
chapter 20 is 10,000 lines long, but the author's working out how to split it up into digestible chunks... 8)
Its about 23 pages, but with 14 images. I think you should get it, you will feel a lot more confident trying to decide what to do imho.
Emile Vrijdags
An excellent book for the problem, but the recommendations it makes (and other recommendations in this thread) all share a common requirement: if you want to refactor this file for all of your branches, then the only way you can do this is freeze the file for all branches and make the initial structural changes. There's no way around that. The book outlines an iterative approach for extracting sub-classes safely with no automatic refactoring support, by creating duplicate methods and delegating calls, but all of this is moot if you can't modify the files.
Dan Bryant
I couldn't agree more. This book has all the techniques you need to tackle these issues.
@Martin, the book is excellent but it does rely quite heavily on the test, refactor, test cycle which may be quite hard from where you are now. I've been in a similar situation and this book was the most helpful one I found. It's got good suggestions for the ugly problem you have. But if you can't get a test harness of some sort into the picture all the refactoring suggestions in the world won't help you.
@moz: I agree the book does rely on there being tests for the code before refactoring but I think in this situation the OP needs all the help he can get and this book is a good start.
Tony, I agree. I'm little cautious because I've found in the past that some ugly code is not amenable to testing. Often with an an application that has never had any kind of automated testing applied to it, and usually symptomatic of a low priority given to testing in general.In that situation I would go with whatever testing you can do easily, and try some of the other modification approaches, keeping the desire to have automated testing available in the future in the back of your mind. In other words, make testability another goal rather than a precondition.
+19  A: 

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:

  1. 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.

  2. 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.

  3. 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.

+1 for item 2 :-)
+57  A: 

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 :)

Brian Rasmussen
It smells a lot: it smells like the Blob anti-pattern is in da house... His favorite meal is spaghetti code: :-)
@jdehaan: I was trying to be diplomatic about it :)
Brian Rasmussen
+1 @Brian for automated verification prior to refactor.
+1 From me too, I don't dare touch even complex code I've written without tests to cover it.
Danny Thomas
+3  A: 

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).

As always, I would like to get an explanation for the downvote.

Correct me if I understood the question wrong.

Why can't you split source as functions or classes (seperate .h/.cpp files) and include them as headers? Surely there must be reuse of some functionality.

That would be a start.

There is more than one version of the project, so splitting the file just like that will cause confusion. The questioner wants to know how he can split the file while causing very little confusion.
+12  A: 

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.


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.

+1 an alternative to the solution i proposed, with the same idea : change the API in order to separate the big problem into small ones.
+7  A: 

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.


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.

Everytime i hear "from scratch" in topic about refactoring I kill a kitten!
Just out of curiosity, what's the size of the new codebase ?
I've been in a very similar sounding situation, though the main program loop I had to get to grips with was only ~9000 LOC. And that was bad enough.
+20  A: 

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 agree that the goal should be to have one version of the software, but would it not be better to use config files(runtime) and not compile time custumization
Esben Skov Pedersen
Or even "config classes" for each customer's build.
I figure that compile-time or run-time configuration is functionally irrelevant, but I don't want to limit the possibilities. Compile-time configuration has the advantage that the client can't hack around with a configuration file to activate extra features, as it puts all configuration in the source tree instead of as deployable "textual object" code. The flip side is that you tend toward AlternateHardAndSoftLayers if it's run-time.
+1  A: 

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.

+1  A: 

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.

+5  A: 

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.


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


#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_3 /* you also need component 3 for component 1 */

#if defined(Activate_Component_2)
#define _REQUIRES_COMPONENT_15 /* you also need component 15 for this component  */

/* later on in the header */

#include "component_1.cpp"

#include "component_2.cpp"

#include "component_3.cpp"

#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.

Elf King
This looks like the works-but-initially-painful results of experience.
Actually, it is a technique that was used in Borland C++ compilers to emulate Pascal style Uses for managing header files. Especially when they did the initial port of their Text-based Windowing system.
Elf King
+11  A: 

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.

Michael Stum
+1 for factoring out and #include back in. If you did this for all 10 branches (bit of work there, but manageable) you would still have the other problem, that of posting changes across all your branches, but *that* problem wouldn't have expanded (necessarily).Is it ugly? Yes it still is, but it might bring a small bit of rationality to the problem. Having spent several years doing maintenance and servicing for a really, really big product, I know that maintenance involves a lot of pain. At the very least learn from it, and serve as a cautionary tale to others.

"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
No, there is no big switch actually. The sentence is just the closest I can come to describing this mess :)
+24  A: 
  1. 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.

  2. 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.

Steve Jessop
+1 for specific solution proposal
As for merging: I've looked at GIT and I've looked at SVN and I've looked at Perforce and let me tell you that nothing I've seen anywhere beats AccuRev+Araxis for what we do. :-) (Although GIT can do this [ ] and AccuRev can't - everyone has to decide for himself if this is part of merging or of history analysis.)
Fair enough - maybe you already have the best tool available. Git's ability to merge a change which occurred in File A on branch X, into File B on branch Y, ought to make it easier to split branched files, but presumably the system you use has advantages you like. Anyway, I'm not proposing you switch to git, just saying that SCC does make a difference here, but even so I agree with you that this can be discounted :-)
Steve Jessop

Stop coding. Go to beach

Stop posting. Go to beach.
Do not collect $200
+3  A: 


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.

David Conde
+1  A: 

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.


I think the easiest way to track the history of source when splitting a file would be something like this:

  1. 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.
  2. Delete code from these copies. That should not break the history for the lines you keep.
Christopher Creutzig
"using whatever history-preserving copy commands your SCM system provides" ... bad thing it does not provide any
Too bad. That alone sounds like a good reason to switch to something more modern. :-)
Christopher Creutzig

I think what I would do in this situation is bit the bullet and:

  1. Figure out how I wanted to split the file up (based on the current development version)
  2. Put an administrative lock on the file ("Nobody touch mainmodule.cpp after 5pm Friday!!!"
  3. Spend your long weekend applying that change to the >10 maintenance versions (from oldest to newest), up to and including the current version.
  4. Delete mainmodule.cpp from all supported versions of the software. It's a new Age - there is no more mainmodule.cpp.
  5. 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?


Scrap it, start from scratch, that will save your employer a lot of headache and money and possible bankrupcy and you'll be the Hero. But you gotta have balls to tell them.

+13  A: 

Confucius say: "first step to getting out of hole is to stop digging hole."

+1 for smile :-)
same here lol +1
+3  A: 

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".

Brooks Moses

This is a hard and interesting refactoring.

First, separate the implementation from the interface. Turn this huge file into an empty shell which just forward the call and the parameters. This way, you can create component with limited responsability without any caller being affected (they still call the huge file/module/class).

To this completely, you also need to hunt for the creation time of your new potential component. Depending on how the constructor are sent, this can be quite tricky with stacking of parameters until you have all of them.

then, you can hunt for the callers and make them call your component. That's the easy part.


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.

Jesper Smith

You are worried about the size of the file.

Historically, file size for C programs was determined by the limits of the machine, a PDP11/40. The one I used could handle a file with a 4096 byte maximum. In order to get around this the C compiler used #include and invented .h files to help the linker and segmented loader, since the loader had to dynamically swap (hence the segment registers in the intel architecture).

Small files solved the problem but left an historical legacy. Programmers now believe that small files are the only way to program. You have a machine with 4 gigabytes (vs 8 kilobytes on the 11/40). You have a machine with 3 billion instructions per second (vs 500 kilo instructions on the 11/40). You have a compiler that can block optimize code it can see (as opposed to linking .o files which it cannot see). You have a machine that is bandwidth limited by disk I/O but you want to create 500 tiny .c, .h, and .o files, possibly multiple times with the .h includes.

There is absolutely nothing wrong with a large C file. The compiler can heavily optimize, the disk I/O is minimal, the linker time disappears, the editor can find things trivially without a fancy IDE, ...

11000 lines is a trivial file for today. Free yourself from history.

-1 11kloc is still unmaintainable, and Android builds do not appear to be I/O bound
Hmmm. He said the FILE was 11kloc. Suppose it contains 1000 functions.Why would 1000 files make it "maintainable"?
The linker doesn't even look at .h files. You're forgetting that 11,000 lines of code don't play nice when multiple people are trying to merge their changes into it. Computing power and IO speed have little to nothing with regards to code maintainability. Proper organisation and compartmentalisation of code is much more important than the speed at which your compiler can read/compile the file.
+2  A: 

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.

Paul Rubel
I think others proposed similar things. This is short and to the point and I think this may be a valid starting point for the original problem.

Another book you may find interesting/helpful is Refactoring.


Let me guess: you work for PayPal.


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.

Channing Walton

Just guessing, if this code is serving 10 customers and contains code variants, you may have lot of code clones with variants for specific customers

I'd be very tempted to run a clone detector on your 11,000 line file. (In fact, if you send it to me, I'll do that with my C++ capable clone detector [see bio] and send you the answer).

That would show any clones, and how those clones varied. With that information, it might be fairly easy to refactor the code.

Ira Baxter
+1  A: 

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 I understand, the problem is this: if you bite the bullet and refactor, you can't carry patches between the versions anymore. SCC might be perfectly set up.
@peterchen - exactly the problem. SCCs do merging on the file level. (3-way merges) If you move code around between files you will have to start to manually fiddle modified code blocks from one file to another. (The GIT feature someone else mentioned in another comment is just good for history, not for merging as far as I can tell)
+2  A: 
  1. Do not ever touch this file and the code again!
  2. Treat is like something you are stuck with. Start writing adapters for the functionality encoded there.
  3. Write new code in different units and talk only to adapters which encapsulate the functionality of the monster.
  4. ... if only one of the above is not possible, quit the job and get you a new one.
+/- 0 - seriously, where are you people living that you'd recommend quiting a job based on a technical detail like this?
+2  A: 

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:

  1. Write code to exhaustively test the function in the program in question. Sounds like you won't already have this in hand...
  2. 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.
  3. Refactor the code identified in 2. into a separate class.
  4. Rerun your tests to ensure nothing got broken.
  5. 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.

Steve Townsend