Universal less for pointers in C++ standard

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Two pointers can be compared with using the comparison function objects less, greater etc. Otherwise, using blanket operator< etc, this is only possible if the pointers point to elements of the same array object or one past the end. Otherwise, results are unspecified.

20.3.3/8 in C++03

For templates greater, less, greater_equal, and less_equal, the specializations for any
pointer type yield a total order, even if the built-in operators <, >, <=, >= do not.

No need to explicitly specialize and manually casting to size_t: That would lower the portability even, since the mapping of reinterpret_cast from pointers to integers is implementation defined and is not required to yield any order.

Edit: For a more detailed answer, see this one.

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