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2788.basic_string range mutators unintentionally require a default constructible allocator

Section: 27.4.3.7.2[string.append], 27.4.3.7.3[string.assign], 27.4.3.7.4[string.insert], 27.4.3.7.6[string.replace]Status:C++17Submitter: Billy O'Neal IIIOpened: 2016-10-25Last modified: 2017-07-30

Priority:2

View all otherissues in [string.append].

View all issues withC++17 status.

Discussion:

Email discussion occurred on thelib reflector.

basic_string's mutation functions show construction of temporarybasic_string instances, without passing an allocator parameter. This says thatbasic_string needs to use a default-initialized allocator, which is clearly unintentional. The temporary needs to use the same allocator the currentbasic_string instance uses, if an implmentation needs to create a temporary at all.

libc++ already does this; I believe libstdc++ does as well (due to the bug report we got from a user that brought this to our attention), but have not verified there. I implemented this in MSVC++'s STL and this change is scheduled to ship in VS "15" RTW.

[2016-11-12, Issaquah]

Sat AM: Priority 2

Alisdair to investigate and (possibly) provide an alternate P/R

[2017-02-13 Alisdair responds:]

Looks good to me - no suggested alternative

[Kona 2017-02-28]

Accepted as Immediate.

Proposed resolution:

This wording is relative to N4606.

1. In 27.4.3.7.2[string.append], add the allocator parameter to the range overload temporary:

   template<class InputIterator>  basic_string& append(InputIterator first, InputIterator last);

   -19-Requires:[first, last) is a valid range.

   -20-Effects: Equivalent toappend(basic_string(first, last, get_allocator())).

   -21-Returns:*this.

2. In 27.4.3.7.3[string.assign], add the allocator parameter to the range overload temporary:

   template<class InputIterator>  basic_string& assign(InputIterator first, InputIterator last);

   -23-Effects: Equivalent toassign(basic_string(first, last, get_allocator())).

   -24-Returns:*this.

3. In 27.4.3.7.4[string.insert], add the allocator parameter to the range overload temporary:

   template<class InputIterator>  iterator insert(const_iterator p, InputIterator first, InputIterator last);

   -23-Requires:p is a valid iterator on*this.[first, last) is a valid range.

   -24-Effects: Equivalent toinsert(p - begin(), basic_string(first, last, get_allocator())).

   -25-Returns: An iterator which refers to the copy of the first inserted character, orp iffirst == last.

4. In 27.4.3.7.6[string.replace], add the allocator parameter to the range overload temporary:

   template<class InputIterator>  basic_string& replace(const_iterator i1, const_iterator i2,                        InputIterator j1, InputIterator j2);

   -32-Requires:[begin(), i1),[i1, i2) and[j1, j2) are valid ranges.

   -33-Effects: Callsreplace(i1 - begin(), i2 - i1, basic_string(j1, j2, get_allocator())).

   -34-Returns:*this.