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Date: Wed, 9 Feb 2022 15:11:50 -0500
From: Rich Felker <dalias@...c.org>
To: Pinghao Wu <xdavidwuph@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] fgetws: fix checking for fgetwc errors
On Thu, Feb 10, 2022 at 02:47:36AM +0800, Pinghao Wu wrote:
> This corrects checking for fgetwc errors by arming dummy errno before
> each invocation, and checking errors only if it returns WEOF.
> ---
> src/stdio/fgetws.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/src/stdio/fgetws.c b/src/stdio/fgetws.c
> index b08b3049..edcd769b 100644
> --- a/src/stdio/fgetws.c
> +++ b/src/stdio/fgetws.c
> @@ -12,18 +12,19 @@ wchar_t *fgetws(wchar_t *restrict s, int n, FILE *restrict f)
>
> FLOCK(f);
>
> - /* Setup a dummy errno so we can detect EILSEQ. This is
> - * the only way to catch encoding errors in the form of a
> - * partial character just before EOF. */
> - errno = EAGAIN;
> + wint_t c;
> for (; n; n--) {
> - wint_t c = __fgetwc_unlocked(f);
> + /* Setup a dummy errno so we can detect EILSEQ. This is
> + * the only way to catch encoding errors in the form of a
> + * partial character just before EOF. */
> + errno = EAGAIN;
> + c = __fgetwc_unlocked(f);
> if (c == WEOF) break;
> *p++ = c;
> if (c == '\n') break;
> }
> *p = 0;
> - if (ferror(f) || errno==EILSEQ) p = s;
> + if (c == WEOF && (ferror(f) || errno==EILSEQ)) p = s;
>
> FUNLOCK(f);
>
> --
> 2.35.1
Thanks. I didn't get from your previous patch for fgetwc that there
was a problem in fgetws that you were trying to fix. Now it makes a
lot more sense.
I think the above has at least one bug though: errno and c will both
be uninitialized if n was zero going into the loop (possible if the
initial value of n at function entry was 1). The error handling logic
should probably just be moved inside the loop instead of breaking out
to do it.
Rich
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