Re: avoid atoi, when possible; int overflow -> heap corruption

From: Jeff King <peff@peff.net>
Date: May 22, 2006, 13:37 UTC
Message-ID: <20060522133746.GA12302@coredump.intra.peff.net>
In-Reply-To: <118833cc0605220616t75a182b1oa404d5efe8a1f5d9@mail.gmail.com>

On Mon, May 22, 2006 at 09:16:50AM -0400, Morten Welinder wrote:

> atoi has undefined behaviour for "99-and-any-suffix".  You might
> get lucky and get back 99, but you might also get a random value
> or a core dump.

Where do you get that from? The standard claims that it converts "the
initial portion of the string pointed to" (7.20.1.2). Furthermore, atoi
is equivalent to strtol with a base of 10 (with the exception of range
errors). From 7.20.1.4, paragraph 2:
  The strtol [...] functions [...] decompose the input string into three
  parts: an initial, possibly empty, sequence of white-space characters
  [...], a subject sequence resembling an integer represented in some
  radix determined by the value of base, and a final string of one or
  more unrecognized characters...
If no conversion can be performed (i.e., you feed it garbage with no
number), zero is returned.

atoi does NOT handle range errors, however; the behavior is undefined in that case. In practice, I expect most implementations do some sort of wrapping.

-Peff