Hacker News Reader

That's a derp on my part. Fixed. Thanks. Clearly, this stuff is incredibly complex.

Indeed, errno is not cleared by successful calls, so you can't check it for success.

After a short write your only legitimate course of action is to advance the pointer and write again.

You can set errno to 0 and see if it changes.

The syscall is allowed to set it even in case of success.

This is sort of right, but the behaviour is a bit subtle. errno should never be set to zero by any POSIX-compliant syscall or library call. However it may be set to something (which is non-zero) on a successful call. Ref: https://pubs.opengroup.org/onlinepubs/9699919799/functions/e...

I'm not sure there is any guarantee that a function that completes successfully hasn't changed the value of errno anyway.

Yeah, I didn't mean to imply that you can ignore the return value.

note, while this might be true for write it is not true for fwrite

> The fwrite() function shall return the number of elements successfully written, which may be less than nitems if a write error is encountered

> if a write error occurs, the error indicator for the stream shall be set, and errno shall be set to indicate the error