Re: [boost] [string_ref] string literal constructor

2013/11/7 Gavin Lambert

On 7/11/2013 05:19, Quoth Marshall Clow:

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On Nov 2, 2013, at 10:49 PM, Antony Polukhin wrote:

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)

I was thinking about pointing that out earlier but I assumed that resolving that issue was what he meant by the "strlen_s" comment.

<...> Yes, I meant strlen_s. This function in not in Standard so some pseodocode `std::min(N, strlen(str))` was provided to describe the idea.

While I mostly agree with this, it is probably just as common to have a char buffer on the stack that you *think* is null terminated, but might not be. (Particularly if the classic "strncpy" has been involved at some point.) That's where having this sort of constructor could be beneficial, to act as a backstop against such issues.

Though personally I'm still inclined to leave it explicitly up to the application -- the app code needs to be much more aware of what it's doing if it's intentionally passing around (potentially) non-terminated strings; and if it's accidental then it's a bug that should be fixed immediately (eg. with a safe_strncpy) rather than being quietly resolved by a library.

This is one of the good points. But from the view of usability user may assume that library will determinate the size in this situation: const char s[] = {'0', '1', '2'}; /* User knows that this is not zero terminated*/ string_ref test(s); // Size of array is determinated at this point. Why not have {ptr, 3}? Questions about nonzero terminated strings arise quite often. On the other hand, if we apply the strlen_s then users may be surprised by the following: const char s[] = {'0', '1', '2', '\0', '\1'}; /* User knows that this has fixed size*/ string_ref test(s); // Size of array is determinated at this point. Why *we have* {ptr, 3}? Looks like there is no solution that will satisfy all the users. -- Best regards, Antony Polukhin