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Re: Defect Report: Wordings on basic_string::data() disallow small-string optimization

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> You cannot make normative conclusions from this code, because it invokes
> undefined behaviour. This is so, because the expression
>
> x = std::move(str)
>
> calls a function that (potentially) invalidates the pointer returned
> fromstr.data(), based on 21.4.1 [string.require] p6:
>
> "References, pointers, and iterators referring to the elements of a
> basic_string sequence may be invalidated by the following uses of that
> basic_string object:
> � as an argument to any standard library function taking a reference to
> non-const basic_string as an argument.(footnote)
> � Calling non-const member functions, except operator[], at, front,
> back, begin, rbegin, end, and rend."

In the previous reply, I took "standard library function taking a
reference to ..." as std::move() in the above expression.

But if you are referring operator=(basic_string&&) itself as the
trigger of invalidation, it seems impossible to show the problem with a
valid C++ code example, because comparison of pointers is the only way
in C++ to examine the effect on data().
>
> data(): points at the array whose first element was pointed at by str.data()

Returning to the original DR;
It is not possible to confirm the above effect of data() if small-string
optimization is implemented, because data() may point an small array
which is distinct for each basic_string instance to decrease the number
of allocation.

--
k_satoda


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Re: Defect Report: Wordings on basic_string::data() disallow small-string optimization Kazutoshi Satoda <k_satoda@f2.dion.ne.jp> - 2011-08-28 08:42 -0700
  Re: Defect Report: Wordings on basic_string::data() disallow small-string optimization Daniel Krügler<daniel.kruegler@googlemail.com> - 2011-08-28 11:07 -0700

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