Re: [PATCH] strbuf: clear errno before calling getdelim(3)

From: Simon Ruderich <simon@ruderich.org>
Date: Aug 11, 2017, 07:50 UTC
Message-ID: <20170811075059.nn6lru7uy6s6vpza@ruderich.org>
In-Reply-To: <cd49ce13-db87-89c1-77e7-998fdb9442c3@web.de>

On Thu, Aug 10, 2017 at 10:56:40PM +0200, René Scharfe wrote:

> getdelim(3) returns -1 at the end of the file and if it encounters an
> error, but sets errno only in the latter case.  Set errno to zero before
> calling it to avoid misdiagnosing an out-of-memory condition due to a
> left-over value from some other function call.

getdelim(3p) doesn't explicitly forbid changing the errno on EOF:

    If no characters were read, and the end-of-file indicator for
    the stream is set, or if the stream is at end-of-file, the
    end-of-file indicator for the stream shall be set and the
    function shall return −1. If an error occurs, the error
    indicator for the stream shall be set, and the function shall
    return −1 and set errno to indicate the error.

So a valid implementation could still set errno on EOF and also on another error (where it's required to set errno).

I don't think that it matters in practice, but the "most" correct way to handle this would be to check if feof(3) is true to check for the non-errno case.

Regards Simon

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