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Re: Passing 0 for number of bytes to be scanned in memchr
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: Aditya K <hiraditya at msn dot com>
- Cc: "libstdc++ at gcc dot gnu dot org" <libstdc++ at gcc dot gnu dot org>
- Date: Thu, 16 Feb 2017 12:12:59 +0000
- Subject: Re: Passing 0 for number of bytes to be scanned in memchr
- Authentication-results: sourceware.org; auth=none
- References: <KL1PR0601MB2021B092943830C1BB1221F0B65A0@KL1PR0601MB2021.apcprd06.prod.outlook.com>
On 16/02/17 11:38 +0000, Aditya K wrote:
Hi Jonathan,
I see that in char_traits<char>::find, we check if the number of bytes to be scanned is zero. I think memchr handles that case already but I do not have
any reference to point out to. The documentation does not explicitly mention what happens when 'n' is zero. If n==0 is already handled then
we can safely remove this check. Please let me know your thoughts.
269 static const char_type*
270 find(const char_type* __s, size_t __n, const char_type& __a)
271 {
272 if (__n == 0)
273 return 0;
274 return static_cast<const char_type*>(__builtin_memchr(__s, __a, __n));
275 }
If __s is a null pointer then passing it to memchr is undefined.
I'm not 100% sure, but I don't think basic_string::find has the same
restriction, so we need to handle the case where it's null and avoid
calling memchr.