On 4/13/2011 12:49 PM, Nevin Liber wrote:
x< y has a specified order for pointers pointing within the same array or object, but is undefined for pointers not pointing in the same array or object.
std::less guarantees a total ordering for all pointers, but does not specify what that ordering is, even for pointers pointing within the same array or object (as the pointer specialization is not required to use x< y to do any comparisons).
To make is_from work, we need a total, *specified* ordering for all pointers. I see no way to combine the above two to get a total specified ordering.
There is s bug in the standards because according to 5.2.10/4 a pointer can be converted to an integral type to later be ordered. i.e.: struct Silly { bool is_from(const char* p) { return !std::less<long>()(reinterpret_cast<long>(p), reinterpret_cast<long>(buffer)) && std::less<long>()(reinterpret_cast<long>(p), reinterpret_cast<long>(buffer + sizeof(buffer))); } char buffer[1024]; }; -Phil