From: Rich Felker <dalias@libc.org>
To: "wangjianjian (C)" <wangjianjian3@huawei.com>
Cc: "musl@lists.openwall.com" <musl@lists.openwall.com>,
"Songyunlong (Euler)" <yunlong.song@huawei.com>
Subject: Re: [PATCH] ftello: Need adjust file offset before switching to write
Date: Wed, 18 Dec 2019 08:46:36 -0500 [thread overview]
Message-ID: <20191218134636.GM1666@brightrain.aerifal.cx> (raw)
In-Reply-To: <07082d7e15024b06ba261fbb4e29eac5@huawei.com>
On Wed, Dec 18, 2019 at 10:18:16AM +0000, wangjianjian (C) wrote:
> Consider below code flow:
>
> FILE *fp = fopen("foobar", "w+");
> fputs("hello", fp);
> rewind(fp);
> fgetc(fp);
> ungetc('x', fp);
> fputs("world", fp);
^^^^^^^^^^^^^^^^^^^
This line produces UB. You can't perform a write after ungetc without
an intervening successful seek (or hitting EOF).
Rich
next prev parent reply other threads:[~2019-12-18 13:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-18 10:18 wangjianjian (C)
2019-12-18 13:46 ` Rich Felker [this message]
2019-12-19 2:47 ` 答复: [musl] " wangjianjian (C)
2019-12-19 3:03 ` Rich Felker
2019-12-19 3:19 ` 答复: " wangjianjian (C)
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