https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109305
--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #5)
> Removing it would make the code less efficient and more complex.
In fact, I don't even see how it would be possible, except by making *another*
copy, e.g.
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -1588,20 +1588,33 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
_M_destroy(_M_allocated_capacity);
_M_data(_M_use_local_data());
_M_set_length(0);
+ std::__alloc_on_copy(_M_get_allocator(),
+ __str._M_get_allocator());
}
else
{
+ auto __backup_alloc = _M_get_allocator();
+ std::__alloc_on_copy(_M_get_allocator(),
+ __str._M_get_allocator());
const auto __len = __str.size();
- auto __alloc = __str._M_get_allocator();
- // If this allocation throws there are no effects:
- auto __ptr = _Alloc_traits::allocate(__alloc, __len + 1);
- _M_destroy(_M_allocated_capacity);
+ pointer __ptr;
+ __try {
+ __ptr = _Alloc_traits::allocate(_M_get_allocator(),
+ __len + 1);
+ } __catch (...) {
+ std::__alloc_on_copy(_M_get_allocator(), __backup_alloc);
+ __throw_exception_again;
+ }
+ _Alloc_traits::deallocate(__backup_alloc, _M_data(),
+ _M_allocated_capacity + 1);
_M_data(__ptr);
_M_capacity(__len);
_M_set_length(__len);
}
}
- std::__alloc_on_copy(_M_get_allocator(), __str._M_get_allocator());
+ else
+ std::__alloc_on_copy(_M_get_allocator(),
+ __str._M_get_allocator());
}
#endif
this->_M_assign(__str);
This makes the code much worse, and slower, and still has a copy (the
__backup_alloc) variable.
