[wmobit]

The alloca usage here terrifies me.

[burgerbrain]

That is a good point. I don't know if write has a limit on 'count' (I can't find anything saying that it does), but if it's simply "whatever you can fit in size_t" then you certainly want to be careful about putting that on your stack. Failed alloca's don't really give you any indication, though you might sigsegv later.

[sickill]

What would you suggest instead then? I'm not C programmer.

[burgerbrain]

Avoid the allocation entirely. Use writev for example (or just use multiple 'write's, if you don't care about it being atomic).

[sickill]

Thx. Improved version in master: https://github.com/sickill/stderred/blob/master/stderred.c