Re: basic_string ctor

Stephen Howe wrote:
>> They're not the same in C, which has no real concept of a string.
>
> It most certainly does.
> Admittedly it has limitations (can't have a string of '\0''s,
> strlen() is O(N) not O(1), all memory managment of it is manual) but
> it has been like that since the early days.

Which doesn't make it right - C strings are lame at best and we all know it.

>
>> In the (IME far more common) case where the distinction is merely an
>> artifact of C's poor string concept, I'd prefer the C++ library to
>> simply accept 0 as an empty string.
>
> It has nothin to do with C's poor string concept.
> It has everything to do with the fact that NULL or 0 in pointer
> situations is regarded as an invalid pointer for all types.

But here we're converting from a pointer to an object. The validity of that
pointer is entirely up to the object's constructor to decide. I'm sure 10's
of 1000's of C++ programmers have designed classes that take a pointer
paramter to their constructor and provide some reasonable default behavior
if the pointer is null. It's really not that radical an idea.

>
> As shown in answer to Duane, you can make a valid pointer to an empty
> string and a NULL pointer both construct a std::string as empty.
>
> But if you fold this distinction in std::string's constructor, so
> NULL will silently construct an empty std::string, then in the
> situation where the pointer being NULL is an error in the program,
> this will silently pass over this.

Yep. And in the 1000's of cases where the 0 isn't an error it'll frustrate
and confuse the programmer when the seemingly reasonable std::string(0)
crashes their program.

Neither solution is perfect, and opinions vary as to which is "better" or
"safer". Most opinions I've encountered agree that C++ would be easier to
learn and safer for most programmers to use if there was less undefined
behavior.

-cd


.

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