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From: Bruce Richardson <bruce.richardson@intel.com>
To: David Marchand <david.marchand@redhat.com>
Cc: Kevin Laatz <kevin.laatz@intel.com>, dev <dev@dpdk.org>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	dpdk stable <stable@dpdk.org>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH] net/ring: fix unchecked return value
Date: Wed, 23 Sep 2020 11:25:32 +0100
Message-ID: <20200923102532.GA1760@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <CAJFAV8wTe+DbmrYGxzm0Oydu+v1jvwCm8Zhw=Ha9Evdqjt-RVQ@mail.gmail.com>

On Wed, Sep 23, 2020 at 11:43:31AM +0200, David Marchand wrote:
> On Wed, Sep 23, 2020 at 11:39 AM Bruce Richardson
> <bruce.richardson@intel.com> wrote:
> > I think a more standard way of checking for trailing chars is to use %n
> > which stores the number of chars processed. Then check that against
> > strlen.
> >
> > For example something like:
> >
> > if (sscanf(value, "%p%n", args, n) != 1 || n != strlen(value)) {
> >   /* do error handling */
> > }
> >
> 
> The man is a bit scary about %n:
> 
> The C standard says: "Execution of a %n directive does not increment
> the assignment count returned at the completion of execution" but the
> Corrigendum seems to contradict this.  Probably it is wise not to make
> any assumptions on the effect of %n conversions on the return value.
> 

That's not in the man page on my system (Ubuntu 20.04):

n     Nothing is expected; instead, the number of characters  consumed  thus  far
      from  the input is stored through the next pointer, which must be a pointer
      to int.  This is not a conversion and does not increase the count  returned
      by  the  function.  The assignment can be suppressed with the * assignment-
      suppression character, but the effect on the  return  value  is  undefined.
      Therefore %*n conversions should not be used.


  parent reply	other threads:[~2020-09-23 10:25 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-22 17:20 [dpdk-stable] " Kevin Laatz
2020-09-23  8:06 ` [dpdk-stable] [dpdk-dev] " David Marchand
2020-09-23  9:39   ` Bruce Richardson
2020-09-23  9:43     ` David Marchand
2020-09-23 10:04       ` Kevin Laatz
2020-09-23 10:25       ` Bruce Richardson [this message]
2020-09-25 12:43 ` [dpdk-stable] " Ferruh Yigit
2020-10-01 14:14   ` Kevin Laatz
2020-10-01 14:51     ` Ferruh Yigit
2020-10-01 17:09 ` [dpdk-stable] [PATCH v2] " Kevin Laatz
2020-10-12 11:57   ` Ferruh Yigit
2020-10-12 12:45     ` Bruce Richardson
2020-10-12 13:04       ` Ferruh Yigit
2020-10-12 13:11         ` Bruce Richardson
2020-10-13 13:07   ` [dpdk-stable] [PATCH v3] " Kevin Laatz
2020-10-13 17:23     ` Ferruh Yigit

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