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You've just inherited a legacy C++ codebase, now what?

gaultier.github.io

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Re: You've just inherited a legacy C++ codebase, now what?

#21

Post by Joel_Mckay »

Night_Thastus wrote: post #5
keepamovin wrote: post #3

It's funny. My first step would be 0. You reach out to the previous maintainers, visit them, buy them tea/beer and chat (eventually) about the codebase. Learned Wizards will teach you much. But I didn't see that anywhere. I think the rest of the suggestions (like get it running across platform, get tests passing) are useful stress tests likely to lead you to robustness and understanding however. But I'd def be going…

IME, this only works if you can get regular help from them. A one-off won't help much at all.

I've always found discussing why former employees left a project incredibly enlightening. They will usually explain the reality behind the PR given they are no longer involved in the politics. Most importantly they will often tell you your best case future with a firm.

Normally, employment agreements specifically restrict contact with former staff, or discussions of sensitive matters like compensation packages.

C++ is like any other language, in that it will often take 3 times longer to understand something than re-implement the same. If you are lucky, than everything is a minimal API lib, and you get repetitive examples of the use cases... but the cooperative OSS breadcrumb model almost never happens in commercial shops...

Legacy code bases can be hell to work with, as you end up with the responsibility for 14 years of IT kludges. Also, the opinions from entrenched lamers on what productivity means will be painful at first.

Usually, with C++ it can become its own project specific language variant (STL or Boost may help wrangle the chaos).

You have my sympathy, but no checklist can help with naive design inertia. Have a wonderful day. =)

Re: You've just inherited a legacy C++ codebase, now what?

#22

Post by bluetomcat »

Been there, done that. Don't be a code beauty queen. Make it compile and make it run on your machine. Study the basic control-flow graph starting from the entry point and see the relations between source files. Debug it with step-into and see how deep you go. Only then can you gradually start seeing the big picture and any potential improvements.

Re: You've just inherited a legacy C++ codebase, now what?

#23

Post by mellutussa »

Night_Thastus wrote: post #5
keepamovin wrote: post #3

It's funny. My first step would be 0. You reach out to the previous maintainers, visit them, buy them tea/beer and chat (eventually) about the codebase. Learned Wizards will teach you much. But I didn't see that anywhere. I think the rest of the suggestions (like get it running across platform, get tests passing) are useful stress tests likely to lead you to robustness and understanding however. But I'd def be going…

IME, this only works if you can get regular help from them. A one-off won't help much at all.

> A one-off won't help much at all.

Monumentally disagree. One-off session with a guy who knows the codebase inside out can save you days of research work. Plus telling you all about the problematic/historical areas.

Re: You've just inherited a legacy C++ codebase, now what?

#25

Post by Joel_Mckay »

raverbashing wrote: post #7
keepamovin wrote: post #3

It's funny. My first step would be 0. You reach out to the previous maintainers, visit them, buy them tea/beer and chat (eventually) about the codebase. Learned Wizards will teach you much. But I didn't see that anywhere. I think the rest of the suggestions (like get it running across platform, get tests passing) are useful stress tests likely to lead you to robustness and understanding however. But I'd def be going…

Easier said than done My step 0 would be: run it through an UML tool to get a class diagram and other diagrams. This will help you a lot . > Get the tests passing on your machine Tests? On a C++ codebase? I like your optimism, rs

No one has time to maintain the UML in production.

You may luck out with auto-generated documentation, but few use these tools properly (javadoc or doxygen). =)

Re: You've just inherited a legacy C++ codebase, now what?

#26

Post by aaronbrethorst »

Night_Thastus wrote: post #16

>worry not, by adding std::cmake to the standard library and you’ll see how it’s absolutely a game changer I'm pretty sure my stomach did somersaults on that. But as for the advice: >Get out the chainsaw and rip out everything that’s not absolutely required to provide the features your company/open source project is advertising and selling I hear you, but this is incredibly dangerous. Might as well take that chainsaw…

An optional step locally like pre-commit hooks should be backed up by a required step in the CI. In other words: the ability to run tests locally, lint, fuzz, format, verify Yaml format, check for missing EOF new lines, etc, should exist to help a developer prevent a CI failure before they push.

As far as linters causing thousands of warnings to appear on opening the project, the developer adding the linter should make sure that the linter returns no warnings before they merge that change. This can be accomplished by disabling the linter for some warnings, some files, making some fixes, or some combination of the above.

Re: You've just inherited a legacy C++ codebase, now what?

#28

Post by TwentyPosts »

bun_terminator wrote: post #20
z_open wrote: post #17

Earlier quoted context omitted.

How is that memory safe? Even vector out of bounds index is not memory safe.

You can access a vector with a function that throws an exception if you so desire

You can also just write no code at all if you so desire. It certainly won't cause any memory issues that way. (Hint: What you yourself decide to write or refrain from writing is not the problem. You're not they only person who ever worked on this legacy codebase, and you want guarantees but default, not having to check every line of code in the entire project.)

Re: You've just inherited a legacy C++ codebase, now what?

#30

Post by GuB-42 »

keepamovin wrote: post #3

It's funny. My first step would be 0. You reach out to the previous maintainers, visit them, buy them tea/beer and chat (eventually) about the codebase. Learned Wizards will teach you much. But I didn't see that anywhere. I think the rest of the suggestions (like get it running across platform, get tests passing) are useful stress tests likely to lead you to robustness and understanding however. But I'd def be going…

I wouldn't make it the first step. If you do, you will probably waste their time more than anything.

Try to work on it a little bit first, and once you get stuck in various places, now you can talk to the previous maintainers, it will be much more productive. They will also appreciate the effort.

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