How to read source code learn how to use large system? [closed]

Answer 1

• Do not spend too much time on small details.
• Do not to try to understand the overall system at beginning.
• The point is try to understand one module or component which is relatively "independent", which was added as one entity (feature) in the past. This is usually within the size limit your brain power can cope with because it was done by someone else at one time as one module.
• Your understanding of the overall system will be improved after more components or "pieces" digested and assembled together.
• Tools are very helpful: Doxygen + GraphViz, or a software such as "Understand", call and caller graph in Visual studio, "Find all" and "find all references", etc.

Answer 2

1. Get the code building and running on your dev box.
2. Figure out how the system is used and familiarize yourself with the libraries used. (For example, if you see code with calls to some OpenGL lib, familiarize yourself with that library) Read the system's documentation.
3. I would then find a point of code that will run based on some input. So let's say the system generates output based on some input. I would find the method that initiates the process. Now try to either step through it (could be a pain) or just read the code and try to get a high level overview of what is going on.

I've found that step 3 usually becomes very involved and it is what gives me direction in how to read the code and learn how the system works.

Adding a feature can be a nice idea, but in a large system it could be a pain to even figure out what that feature is. Not only that, any feature you write to learn the system will most likely end up looking like crap because you would have no idea what is where and how the system operates. The feature you want to add though can certainly lead you to the right point in #3 so don't discount that.

-s

Answer 3

Thank you for your answers. Lot's of useful information.

Some tools I can think are:

• grep
• ctags
• cscope
• javadoc (Java)
• DOxygen (C,C++)
• lxr (software toolset for indexing and presenting source code repositories)

Any more suggestion on useful tools?

Answer 4

Find a small spot where you feel comfortable and change it. Ignore the rest; you'll get to learn about it when you need it. Don't feel overwhelmed by the size; every program started with the first line and if it wasn't organized in small, independent bits, it would be impossible to maintain. So there is always a niche for you.

Answer 5

Skim through the code, looking for places where you think you know what is occuring. Read through those sections to see if your initial thought holds up, and then try modifying it to see if you can change it to do something else.

I'd suggest that this be guided slightly by the project roadmap so you can then move on to spotting where new features and bug fixes are so you can contribute in a meaningful manner.

Also, read the documentation and any spin-up documents that may exist (functional specs, requirement specs, etc). This can further help you learn the code ropes quicker :)

Answer 6

Try to reverse engineer the class diagrams.say there is a functionality that gets from A to B.set break point at A, debug,step through and observe the communications,draw the links and the inheritance on your paper.you may also use a sequence diagram. This worked for me to understand specific functionality of a system.