Issue 2235: Undefined behavior without proper requirements on basic_string constructors (original) (raw)

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2235. Undefined behavior without proper requirements on basic_string constructors

Section: 27.4.3.3 [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 27.4.3.3 [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, 27.4.3.3 [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());

27.4.3.3 [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 27.4.3.3 [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 < npospoints to an array of at least n elements of charT.

2. Change 27.4.3.3 [string.cons]/8 as indicated:

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

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