Re: non-const version of std::string::data()
On Nov 25, 12:21 am, "Thomas J. Gritzan" <phygon_antis...@gmx.de>
wrote:
Paavo Helde schrieb:
Paavo Helde <pa...@nospam.please.org> kirjutas:
Juha Nieminen <nos...@thanks.invalid> kirjutas:
[...]
Sorry, forgot to mention *why* they should not mutate. The
reason is that in another thread the client code may held
(const) references or pointers to certain chars inside the
buffer, via the operator[], and it expects them remain valid
while no non-const memmber function is called on the string.
A class with a less promiscuous interface could mutate inner
details also in const member functions.
A const member function shouldn't mutate chars inside the
range of valid characters [begin, end), but the terminating
'\0' will be set outside this range. So I think appending the
zero on a call to c_str() would be correct (that is, reserving
the space for '\0' every time, but only setting the actual
value on a call to c_str).
Exactly. It's an implementation detail.
Note that calls to std::basic_string<>::data() and
std::basic_string<>::c_str() may invalidate iterators,
references and pointers into the string, so an implementation is
not required to even reserve the space. And unless the code
documents otherwise, you have to assume that passing a string to
a function via a string const& also invalidates iterators,
references and pointers into that string. (The string interface
is funny in that regard; calling the const functions data() or
c_str() may invalidate iterators, but calling a non-const
operator[] or at() may not, at least in some circumstances.)
--
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