Answer by Karthik T for Why can't I reinterpret_cast uint to int?

From C++11 Standard(N3376) 5.2.10.1 this document, page 101:

Conversions that can be performed explicitly using reinterpret_cast are listed below. Noother conversion can be performed explicitly using reinterpret_cast.

The only conversion from integral type to integral type allowed is infact if the types are identical.

Others involve pointers.