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### 2235. Undefined behavior without proper requirements on `basic_string` constructors

Section: 21.3.3.3 [string.cons] Status: C++14 Submitter: Juan Soulie Opened: 2013-01-17 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

In 21.3.3.3 [string.cons], I believe tighter requirements should be imposed on `basic_string`'s constructors taking an `s` argument (or, a behavior should be provided for the undefined cases). These requirements are properly stated in the other members functions taking `s` arguments (`append`, `assign`, `insert`,...).

>     basic_string(const charT* s, size_type n, const Allocator& a = Allocator());

Relative to N3485, 21.3.3.3 [string.cons]/6 says "Requires: `s` shall not be a null pointer and `n < npos`", where it should say: "Requires: `s` points to an array of at least `n` elements of `charT`"

>     basic_string(const charT* s, const Allocator& a = Allocator());

21.3.3.3 [string.cons]/8 says "Requires: `s` shall not be a null pointer.", where it should say: "Requires: `s` points to an array of at least `traits::length(s) + 1` elements of `charT`"

Daniel:

I think that 16.4.5.9 [res.on.arguments] p1 b2 basically requires this already, but the wording is indeed worth improving it.

[2013-03-15 Issues Teleconference]

Moved to Review.

The resolution could be worded more cleanly, and there is some concern about redundancy between Requirements and Effects clauses. Consensus that we do want to say something like this for the Requirements though.

[2013-04-18, Bristol]

Move to Ready

[2013-09-29, Bristol]

Apply to the Working Paper

Proposed resolution:

This wording is relative to N3485.

1. Change 21.3.3.3 [string.cons]/6 as indicated:

   >     basic_string(const charT* s, size_type n, const Allocator& a = Allocator());

   > > -6- Requires: `s` shall not be a null pointer and `n < npos` points to an array of at least `n` elements of `charT`.

2. Change 21.3.3.3 [string.cons]/8 as indicated:

   >     basic_string(const charT* s, const Allocator& a = Allocator());

   > > -8- Requires: `s` shall not be a null pointer points to an array of at least `traits::length(s) + 1` elements of `charT`.