Hacker News new | ask | show | jobs
by alinajaf 4929 days ago
Question from a newbie C developer: How can you avoid using malloc? Are you finding some clever way to do everything on the stack? Or are you perhaps allocating a large block of contiguous memory and slicing it up on your own?

I've heard of both of those approaches and they sound pretty hard, so I'd be interested to hear your thoughts/be pointed to good references on the topic. Thanks in advance.
3 comments
psykotic 4929 days ago
A lot of the time, the nature of the data and its lifetime makes specialized allocators easy to use. Not infrequently they can actually be more convenient than malloc/free when you have a bunch of allocations (think nodes in a parse tree) with the same lifetime, so their storage can be released as a single operation. For that example, you can get the same usability with a more traditional malloc/free interface using something like hmalloc, but if the parse tree nodes all occupy the same contiguous block, you get it automatically. And of course it's a lot faster to release a single block (if you release the storage back to the OS, the page manager will still have some per-page work for a virtually contiguous block of memory).

Basically, once you have a nailed down system design, it's usually not any significant extra work to use custom allocators. Where it can suck away your productivity is during iterative design and development where you're still figuring out the different kinds of data, what subsystems exist and who owns what when. But in that scenario, garbage collection is even easier than malloc/free, so it's not a mortal sin to use Bochs or just leak memory (heresy!) if you can get away with it--only temporarily, of course, while you figure out the design.

link
jacquesgt 4929 days ago
There's a large block of memory that's easy to slice up on your own. It's called the BSS section, which is where global and static variables without an initial value are stored. BSS gets zeroed before main() is called.

This isn't possible in all cases, but for embedded software especially it's often possible to create all data structures as global or static variables. The compiler takes care of alignment concerns for you, and you're guaranteed not to have heap issues because you never use the heap. Of course, you can run out of the objects you pre-allocated in BSS, but that's an easier problem to diagnose and fix.

link
qxcv 4929 days ago
The pseudo-C used in the Quake 3 VM had no malloc()[0] and they wrote a frigging AAA game with it. I suggest you check out their source code[1].

[0] http://wiki.ioquake3.org/Getting_the_most_from_Quake3_C#No_M... [1] https://github.com/id-Software/Quake-III-Arena

link