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by derleth 5146 days ago
> That's acceptable for a command-line program that will terminate quickly

No, it isn't; you don't know how quickly the program will terminate, in general, and it only takes one program running longer than you expect to eat a horrible amount of RAM.
2 comments
tptacek 5146 days ago
I'll make a stand for it being bad style to free() memory when in any reasonable run of the program exit() would free just as effectively. This is simply arena allocation; some very excellent, well-regarded C code uses arenas and pools in the same idiom.

The downside to calling free(), apart from performance (malloc/free are extremely expensive), is that messing them up creates bugs that are much worse than simply holding on to some allocator metadata until the program hits exit().

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leif 5146 days ago
The upside to calling free() is that it is a valuable lesson in understanding memory lifetimes for a beginner programmer. You can't know when it's good to omit free until you know what it means.
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derleth 5146 days ago
> messing them up creates bugs

Messing them up exposes bugs that are likely to bite you in other ways. If you can't get malloc()/free() right, you don't really 'get' the flow control/data flow through your program yet and that is a problem.

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tptacek 5146 days ago
Arena allocation is inherently simpler and less error-prone than demand-allocating and demand-freeing. It's not valid to say that arena allocation is "hiding" bugs; what it's doing is foreclosing on the possibility of having those bugs.

Virtually no large project has ever gotten malloc/free completely right in its first revision; for the past 20 years or so, most projects get this wrong to the tune of "remote code execution".

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JoachimSchipper 5146 days ago
Not in general, no, but this particular program doesn't allocate a serious amount of memory (think `ls | less`) and doesn't contain any system calls which can reasonably block[1], so it's extremely unlikely to bite you in this case.

(I do think it's bad style, and would never write this program this way.)

[1] Assuming you stay away from the Zombie^W Network File System. But NFS mounts going away is bad news anyway, this program holding an extra KB of swappable memory doesn't really intensify the pain.

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