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Subject: Re: [boost] RFC: interest in Unicode codecs?
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-07-21 09:35:29

Phil Endecott wrote:
> Stewart, Robert wrote:
> > Sebastian Redl wrote:
> >> Phil Endecott wrote:
> >> >
> >> > Here is an outline of a zero-overhead wrapper for std::string
> >> > that I hope guarantees that *end() == 0:
> >> >
> >> > struct string_with_zero_beyond_end: std::string {
> >> > typedef const char* const_iterator;
> >> > const_iterator begin() const { return c_str(); }
> >> > const_iterator end() const { return c_str() + length(); }
> >> > };
> >>
> >> Not zero-overhead if the string implementation is one (of the
> >> non-existent ones) that doesn't store the NUL internally.
> Is c_str() allowed to be > O(1) ?

Yes, since the entirety of C++98/03's requirements levied against c_str() are shown here:

>From 21.3/5: It can invalidate outstanding iterators, references, and pointers.

>From 21.3.6:

"1 Returns: A pointer to the initial element of an array of length size() + 1 whose first size() elements equal the corresponding elements of the string controlled by *this and whose last element is a null character specified by charT().

2 Requires: The program shall not alter any of the values stored in the array. Nor shall the program treat the returned value as a valid pointer value after any subsequent call to a nonconst member function of the class basic_string that designates the same object as this."

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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