http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51626
Bug #: 51626
Summary: [4.6 Regression] [C++0x] can't use C++98 allocators
with -std=c++0x
Classification: Unclassified
Product: gcc
Version: 4.6.2
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: [email protected]
ReportedBy: [email protected]
#include <memory>
#include <vector>
template <class T>
struct allocator98 : std::allocator<T>
{
template <class U> struct rebind { typedef allocator98<U> other; };
allocator98() { }
template <class U> allocator98(const allocator98<U>&) { };
void construct(T* p, const T& val) { std::allocator<T>::construct(p, val);
}
};
int main()
{
std::vector< int, allocator98<int> > v(1);
}
This fails in c++0x mode because std::__uninitialized_default_n_a() incorrectly
assumes it's OK to call Alloc::construct with a single argument. That is true
for std::allocator in C++0x mode, but not true for most user-defined allocators
written to the C++98 requirements.
This is the cause of https://svn.boost.org/trac/boost/ticket/5538
The bug is fixed in 4.7 because std::allocator_traits provides a default
implementation of construct, ensuring backwards-compatibility with C++98-style
allocators.
A workaround for user-defined allocators is to add:
void construct(pointer p) { return construct(p, value_type()); }
The fix for libstdc++ would be to avoid calling construct with a single
argument, or to backport a minimal version of allocator_traits from 4.7
