Re: [boost] [string_ref] string literal constructor

Subject: Re: [boost] [string_ref] string literal constructor
From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2013-11-06 11:19:02

On Nov 2, 2013, at 10:49 PM, Antony Polukhin <antoshkka_at_[hidden]> wrote:

> 2013/11/3 Michael Marcin <mike.marcin_at_[hidden]>
> 
>> On 11/2/2013 9:43 AM, Marshall Clow wrote:
>> 
>>> On Nov 1, 2013, at 4:42 PM, Michael Marcin <mike.marcin_at_[hidden]> wrote:
>>> 
>>> I noticed string_ref doesn't have a constructor for a string literal.
>>>> Wouldn't this save a call to strlen for a common case?
>>>> 
>>>> Ex.
>>>> 
>>>> template< std::size_t N >
>>>> basic_string_ref( const charT( &str )[N] )
>>>>    : basic_string_ref( str, N-1 )
>>>> {
>>>>    static_assert(N >= 1, "not a string literal");
>>>> }
>>>> 
>>>> string_ref test( "test" );
>>>> 
>>> 
>>> So, what should
>>>        string_ref ( "test\0test" )
>>> do?
>>> 
>>> { ptr, 4 } --> current behavior
>>> { ptr, 9 } --> your suggested behavior
>>> 
>>> 
>> So, what should
>> 
>> const char s[] = {'0', '1', '2'};
>> string_ref test{s};
>> 
>> do?
>> 
>> Neither seems to be very important and can be handled by requiring sane
>> preconditions.
> 
> 
> Marshall, how about adding the following constructor:
> 
> template< std::size_t N >
> basic_string_ref( const charT( &str )[N] )
>    : basic_string_ref( str, std::min(N, strlen(str)) ) /* pseudo code,
> we'll need something like strlen_s */
> {}
> 
> Such constructor won't change the current behavior
> 
> string_ref ( "test\0test" ) // { ptr, 4 }
> 
> but will also work for non-zero terminated fixed length arrays:
> 
> const char s[] = {'0', '1', '2'};
> string_ref test(s); // {ptr, 3}

No, actually, it won't, because the strlen will read past the end of the array, looking for the terminating NULL.
(and that's undefined behavior)

Personally, I'm content with the current situation where
* If you have a NULL terminated string (by far the most common case), the { pointer } constructor works fine.
* If you have something else, you have to use the { pointer, size } constructor.

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists_at_[hidden]>

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