[RFC] Strange line at the end of _M_mutate

[Paolo Carlini]

Hi,

today, while preparing two more testcases for basic_string::assign I noticed
what seems to a me discrepancy. At the beginning of basic_string.h, a comment
says:

      //   1. String really contains _M_length + 1 characters; last is set
      //      to 0 only on call to c_str().  We avoid instantiating
      //      _CharT() where the interface does not require it.

And this is consistent with the implementation of c_str() below.

However, _M_mutate (in basic_string.tcc) ends with:

      _M_data()[__new_size] = _Rep::_S_terminal; // grrr. (per 21.3.4)
    // You cannot leave those LWG people alone for a second.

Now, I cannot find a reference to any relevant issue in 21.3.4 and this line
seems to me not consistent with the comment above.

It is ironic that, were not for this line in _M_mutate, libstdc++/4354 would not
be a bug, *at least* for the implementation of memcopy I'm using (glibc2.2.4):
if _M_mutate would not put that termination char at the end of the _Rep,
otherwise _S_copy_chars (i.e., memcopy) is able to deal with the *specific* copy
pattern necessary for basic_string::assign correctly, as if it were a memmove.

Of course, the real problem with overlapping ranges would have surfaced soon
with replace (we have at least one testcase in the testsuite which gcc-3_0
cannot pass even stripping that line from _M_mutate).

Anyway, do you believe that the final line in _M_mutate is bogus? In that case,
perhaps those two testcases I prepared are not so relevant and _M_mutate should
be patched instead...

Thanks,
Paolo.